Understanding Indoor Air Quality Basics
And The Business Opportunity It Represents
Indoor Air Quality is a growing health problem in North America. It
represents a huge business opportunity for those companies that can
provide solutions to indoor air pollution problems. Understanding IAQ
basics is a key first step to entering this market segment.
This is the first in a series or articles on Indoor Air Quality (IAQ). Estimated annual sales for IAQ products
and services are currently between $2 and $5 billion and are expected to grow to $12 billion a year by
2012.
Many contractors think of IAQ in terms of selling humidifiers and various filter products accessories or
cleaning ductwork. This does represent some of the products and services used for Indoor Air Quality, but
may not represent the solutions needed for many indoor air pollution problems. Other products and
services may be needed to solve most indoor air problems. Contractors such as you can provide many of
the services needed to provide these indoor air solutions. This represents a huge growth opportunity. Other
articles will address the IAQ process, the IAQ business model, the IAQ selling process, the IAQ marketing
plan to support the business plan and sales goals, choosing IAQ & sales best practices and IAQ legal issues.
This article has two objectives. The first is to introduce IAQ fundamentals. Whether you’re planning to
actively pursue IAQ sales opportunities or not, this information is important for contractors to know. Here
are a few quick examples:

Over sizing air conditioning equipment can cause humidity problems in the home.
This in turn can cause mold problems that even a good method of filtration cannot
solve.

Leaky supply and return ducts can cause indoor air pollution.

Pressure problems within the home can also cause indoor air pollution problems and
can interfere with the combustion process in gas appliances. This can cause very
serious health problems.
And these are only three issues. Our industry has positioned itself to be able to solve indoor air comfort
problems. Comfort goes way beyond just heating or cooling a home. Our customers expect their indoor air
to be healthy as well. When we do not meet those expectations, we face unhappy customers. That’s one of
the reasons why many contractors have had or are facing litigation problems over IAQ issues with their
customers. That can be a painful way to get educated on indoor air quality.
The following article is very comprehensive about indoor air quality problems and its consequent health
problems. It also introduces HVAC practices that contribute to these problems as well as possible solutions
to these problems. A future article will focus on the products available to solve indoor air problems.
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This article is an excellent introduction to IAQ basics. You may want to share it with your staff and
employees to help educate them on IAQ issues. It can help understand the importance of applying and
installing HVAC systems correctly. The information is also important from a sales perspective. The
knowledge can help build credibility and confidence with customers.
Not all the solutions to indoor air problems hinge on the heating and air conditioning system. There are
many things a homeowner can do for themselves to improve the quality of the indoor air. This information
can help your employees communicate IAQ issues with customers.
The second objective of this article is to show the state of the IAQ industry and the huge potential it offers
in terms of revenue growth. A future article will introduce the IAQ business model to make sure it is
profitable growth.
Introduction to Indoor Air Quality
According to the American Lung Association, Americans spend an average of 65 percent of their time in
home in what is usually viewed to be a safe haven. However, growing evidence shows that some homes
may be detrimental to the health of those living there. According to the US Environmental Protection
Agency (EPA), indoor air pollution may be two to five times higher than outdoor levels. In some cases
indoor air pollution can be as much as 100 times higher. As a result, the EPA has recognized indoor air
pollution as one of the top five urgent environmental risks to public health.
Exposure to indoor air pollutants such as smoke, dust, pet dander, radon, mold and other pollutants can
pose serious health risks and contribute to respiratory disease, asthma, and even lung cancer. Home
pollutants such as dust mites, pet dander, and mold travel through the air undetected and are known triggers
for asthma. These allergens can be inhaled and enter the respiratory system Pollen and other indoor air
pollutants cause allergy and sinusitis (inflammation of the sinuses). High accumulations of carbon
monoxide, formaldehyde and radon in inadequately ventilated homes pose serious health hazards as well.
In addition, various biological agents found in a home can cause infectious and non-infectious diseases.
Indoor air quality is more of an issue with today’s home construction than what it was in the past. In days
when homes were built fairly loose, fresh air was continually introduced into the home through infiltration.
This diluted any indoor air contaminants so there was less concentration. Construction practices have
changed over the last 30 years to make homes more energy efficient. Homes are built much tighter than in
the past to eliminate infiltration as much as possible and the need to heat or cool that air brought in from
outside. Homes have become considerably tighter resulting in poor ventilation and a marked increase in
pollutants.
Most homes have more than one source of indoor air pollution. For example, pollutants come from tobacco
smoke, building materials, decorating products, home furnishings, and activities such as cooking, and
cleaning. Living in areas with high outdoor levels of pollutants usually results in high indoor levels.
Fortunately there are solutions to these indoor air pollution problems that let people live in a healthier
environment within their homes. These solutions present business opportunities to contractors.
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Respiratory Health
Let’s take a closer at indoor air quality in terms of health.
The Lungs
If something hazardous is ingested into the human stomach, acids and other chemicals can destroy them.
This is not the case for the lungs. The lungs contain some of the most sensitive tissue in the human body.
There are no acids or other chemicals to break down potential hazards taken into the lungs.
The air-sack tissue of the lungs and blood capillaries are meshed closely together in order to efficiently
absorb oxygen into the bloodstream. Airborne pollutants can likewise easily be absorbed into the lung
tissue.
In the nasal area there are the cilia (hairs) and mucus membranes designed to capture airborne particles
before they reach the lungs. This will get larger particles, but smaller particles such as bacteria, viruses and
molds move in and out of the lungs with little impediment. Toxins infiltrate freely.
Another problem with the lungs that relates to pollutants is volume. The greater the volume of
contamination over time, the greater the potential damage. The typical person breathes 22,000 times a day.
This constitutes an enormous volume of air passing through the lungs.
Airborne Allergens
The immune system protects people from diseases by fighting germs like bacteria and viruses. A properly
functioning immune system is designed to identify and destroy many foreign invaders within the body.
Allergies are the result of a hypersensitive immune system. The immune system misidentifies an otherwise
innocuous substance as being harmful and then attacks the substance with ferocity far greater than required.
These substances that trigger allergic reactions are called allergens. An allergy is the body’s immune
reaction to allergens. Allergic diseases are the sixth leading cause of chronic illness in the United States.
Every person has an individual threshold to allergens. This refers to the load the body can resist allergens.
Loads differ depending on genetics, nutrition, etc.
Allergens can be classified into three broad sources: (a) plant pollen, (b) fungi & mold spores and mycelia
fragments, and (c) indoor insect and vertebrate debris that become part of house dust.
Pollens give off a rapid release of proteins when they strike a moist, warm surface like the nasal cavity.
These pollen proteins provoke an immediate immune response. Pollens are seasonal in nature and mainly
come from outdoors. This type of allergic reaction comes usually once a year.
It’s been estimated that 60% of all allergies are caused by molds. A Mayo Clinic study identified nearly all
the chronic sinus infections in 37 million Americans were caused by molds. The tripling of asthma in the
last 20 years has been tied to molds.
About 6 % of the U.S. population has developed allergic reactions to cats. The primary allergen generated
by cats is a protein produced in glands in the skin of the animal. This same protein is in the saliva of the
cat. The protein accumulates in the hair of the animal. As this protein becomes stirred-up, it goes airborne
to react with the nose and lungs of those people who are allergic to cats.
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Dust mites produce thousands of airborne fecal pellets each day. These particles include a digestive
enzyme that can set off a rather severe allergic reaction for those who are sensitive.
Cockroaches produce digestive enzymes and salivary proteins that are allergens. These accumulate in
house dust and go airborne whenever the dust in the house is disturbed.
There are three different allergic reactions, each depending on the location of the allergic inflammation: (a)
Allergic Rhinitis (nasal and upper respiratory inflammation), (b) Sinusitis (inflammation of the sinus
cavities) and (c) Asthma (inflammation of the air bronchial tubes).
Allergens can also causes diseases such as hypersensitivity pneumonitis.
Allergic Rhinitis
About 50 million Americans suffer from rhinitis. People generally develop allergic rhinitis after repeated
exposure over time to an airborne allergen. Allergic rhinitis inflammation can be either seasonal or yeararound. The year-around rhinitis usually comes from indoor allergens (molds, dust mites, etc.) in the air.
Pollens given off by outdoor seasonal plants normally cause the seasonal allergic rhinitis.
Here are some of the symptoms that people with rhinitis experience:
 Less energy and high fatigue factor
 Altered mental capacity
 Lower social functioning
 Higher emotional and physical limitations
 Sleep problems and fatigue
 Loss of concentration
Sinusitis
The sinuses are four sets of air cells located on both sides of the nose. These air cells can become infected
and inflamed. When they do, the problem is called sinusitis. By definition, sinusitis is the bacterial
infection of the paranasal sinuses. These sinus cavities are attached to the nose by very small openings.
These tiny openings can easily be blocked by inflamed tissue or thick secretions caused by allergies or viral
infections. Such conditions become ideal for bacteria to flourish in the warm, moist mucus secretions in
the sinuses. This infection usually leads to nasal congestion, headache, cough, post-nasal drip and fatigue.
Asthma
Asthma is an obstructive lung disease caused by restriction of the airways trigger by various airborne
particulate. It is a chronic condition that can be a life threatening for some if not properly managed. It’s
estimated that 20.3 million people in the United States currently have asthma. Of these an estimated 12
million people have an asthma attack episode at least once a year. It’s estimated that 6.3 million children
under the age of 18 have asthma of which 4 million suffered from an asthma attack in the past year. Here
are some other facts about asthma:

Asthma breathing problems usually happen in ‘episodes’, but the inflammation underlying
asthma is continuous. An asthma episode is a series of events that result in narrowed
airways. These include swelling of the lining, tightening of the muscle and increased
secretion of mucus in the airway. The narrowed airway is responsible for the difficulty in
breathing with the familiar ‘wheeze’.
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
Close to 2 million emergency room visits per year are attributed to asthma.

It’s estimated that 6.3 million children under the age of 18 years of age have asthma; of
which, 4 million suffer from an asthma attack or episode in the past year. The disease is the
most common chronic childhood malady in America.

Only about a quarter of the children with asthma become symptom-free when their airways
reach adult size. The condition persists beyond childhood in 85% of women and in 72 % of
men.

Asthma is characterized by excessive sensitivity of the lungs to various stimuli. Triggers
range from viral infections to allergies, to irritating gases and particles in the air. Here are
different types of triggers:






Respiratory infections, colds
Cigarette smoke
Allergic reactions to pollen, mold, animal dander, feather, dust, food
Indoor and outdoor air pollutants including ozone
Exposure to cold air or sudden temperature change
Excitement/stress
There are three stages in asthmatic reaction.
1. In the first stage the bronchial tubes become inflamed and start producing thick mucus. If the
inflammation is persistent over time, the air tube walls can become permanently thick and
restrictive.
2. In the next stage, the muscles surrounding the bronchial tubes begin to contract causing the air
passages to narrow.
3. In the final stage, the inflamed bronchial tubes become hyper-reactive to allergens or an infection,
which in turn continues the process of inflammation and constriction within the air tubes. This can
become severe and even life threatening.
Chronic asthma is generally triggered by allergens or irritants (such as smoke, fumes and odors) or
infections (cold and flue).
Hypersensitivity Pneumonitis
Hypersensitivity pneumonitis is an inflammation in the lungs caused by exposure to an allergen, usually
organic dust from animal dander, molds or plants. The microorganisms associated with hypersensitivity
pneumonitis are fungi, bacteria and protozoa.
Hypersensitivity pneumonitis can be an acute, recurrent pneumonia with fever, cough, chest tightness and
fluids entering the lungs. Or, it can be a cough that progresses to shortness of breath, fatigue, weight loss
and thickening and scarring of the lungs.
If exposure is eliminated early, there can be improvement or complete recovery. If the allergen exposure is
repeated over time, this can cause permanent lung damage.
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Indoor Air Pollutants and Their Health Effects
Combustion Pollutants
The health effects of combustion pollutants range from headaches and breathing difficulties to death. The
health effects may show up immediately after exposure or occur after being exposed to the pollutants for a
long time. The effects depend upon the type and amount of pollutants and the length of exposure.
These pollutants include carbon monoxide, nitrogen dioxide, particulates and sulfur dioxide. Carbon
monoxide can kill within a short time. The health effects of the other pollutants are generally subtler and
are more likely to affect susceptible people.
Combustion always produces water vapor. Water vapor is not usually considered a pollutant, but it can act
as one. It can result in high humidity and wet surfaces. These conditions encourage the growth biological
pollutants such as mold and bacteria.
Combustion pollutants found indoors include: outdoor air, tobacco smoke, exhaust fumes from cars or lawn
mowers. Some hobby activities such as welding, wood burning and soldering also produce combustion
pollutants. Combustion pollutants can also come from vented or unvented combustion appliances. These
appliances include space heaters, gas ranges, gas water heaters, furnaces, gas clothes dryer, wood or coal
burning stoves and fireplaces.
Gaseous Pollutants
Gaseous pollutants include combustion gases and organic chemicals. Hundreds of different gaseous
pollutants have been detected in indoor air. Gaseous organic components may enter the air from sources
such as cigarette smoke, building materials and furnishings, and the use of products such as paints,
adhesives, dyes, solvents, caulks, cleaners, deodorizers, hobby & craft materials and pesticides.
Health effects vary widely depending on the types and concentrations of the chemicals present. Adverse
effects may include eye & respiratory irritation, and allergic reactions. It can also affect the respiratory
system, immune system, cardiovascular system, reproductive system, and nervous system. Gaseous
pollutants can also cause cancer.
Radon
Radon is a radioactive pollutant, which originates from natural sources such as rock, soil, groundwater and
mineral building materials. Radon itself is a gas, which produce progeny in the form of small particles that
attach to larger particles. Radon progeny can be breathed into the lungs where it may deposit. This
represents the main health hazard from radon.
These pollutants have the potential to cause lung cancer. The risk of lung cancer increases with the radon
level in the air and the frequency and duration of the exposure.
Biological Contaminants
Biological contaminants include bacteria, molds, mildew, viruses, animal dander, house dust mites,
cockroaches and pollen. There are many sources of these pollutants.

Pollens originate from plants
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
Viruses are transmitted by people and animals

Bacteria are carried by people, animals, soil and plant debris

Household pets cause pet dander

Urine from rats and mice is a potent allergen. When it dries, it can become airborne.

Contaminated central air conditioning systems can become breeding grounds for mold, mildew
and other sources of biological contaminates.
By controlling the relative humidity level in a home, the growth of some biological contaminants can be
minimized. A relative humidity of 30 to 50 percent is generally recommended for homes. Standing water,
water-damaged materials or wet surfaces also serve as a breeding ground for molds, mildews, bacteria and
insects. House dust mites grow in damp, warm environments.
Some biological contaminants trigger allergic reactions and some types of asthma. Infectious diseases such
as influenza, measles and chicken pox are transmitted through the air. Molds and mildews release diseasecausing toxins. Some diseases are associated with exposure to toxins from microorganisms that can grow
in home heating and cooling systems and humidifiers.
Symptoms of health problems caused by biological pollutants include sneezing, watery eyes, coughing,
shortness of breath, dizziness, lethargy, fever and digestive problems. Children, elderly people and people
with breathing problems are particularly susceptible to disease-causing pollutants in the indoor air.
Allergic reactions can occur after repeated exposure to a specific biological allergen. However, that
reaction may occur immediately upon re-exposure or after multiple exposures over time. As a result,
people who have noticed only mild allergic reactions, or no reactions in the past, may suddenly find
themselves very sensitive to particular allergens.
There are four very broad types of microorganisms that contaminate indoor air.
Fungi and Molds
Fungi, mold and yeast are all part of the same family. They are classified under a single heading of
‘fungi’. There are thousands of varieties in the fungi family. The most common household molds
are Cladosporium, Penicillium and Alternaria. Borne toxins Molds that are less common but can
produce lethal airborne toxins are Aspergillus versicolor, Memnomiella and Stachybotrys.
Fungi spores can be as small as 3 microns or as large as 140 microns (25 microns are equal to oneone-thousands of an inch). The ideal growth conditions for fungi and molds include moisture,
warmth and food. However, molds are in all types of conditions, especially where there is moisture.
They will feed off any organic material including dust and lint trapped in ventilation systems.
House dust can be the perfect organic meal. With a little moisture, very typical with a central air
conditioning system, they have a perfect breeding ground. They grow and multiply and then blow
all over the home.
Molds can cause allergic reactions, infections and irritation & toxic reactions.
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Health Effects of Molds
Allergic Reactions
Infections
Irritation and Toxic Reactions
Allergic rhinitis, hypersensitivity
pneumonitis, asthma
Colds, TB, flu, legionella, etc.
Mycotoxins, endotoxins, stachybotris,
etc.
Molds may be present throughout an air conditioning system; however, they flourish on the indoor
coil and in the drain pan. This growth occurs downstream of system filters, thus allowing
contaminants to circulate freely through the home.
Molds and fungi produce three types of contaminants.

Fungi and Mold Spores
Spores are, in a sense, seeds from these microorganisms that ride the air currents to new
food sources and growth opportunities. Fungi produce enormous amounts of spores. In a
typical mold colony, millions of spores are pushed into the air each and every day. Spores
can stimulate a rather severe allergic reaction.

Enzyme Filaments (mycelium)
Mold debris secretes enzymes, which can digest carbohydrates and proteins. When these
filaments go airborne, they can be aggressive allergens.

Toxic Gases
Molds are unable to synthesize their own food. They release digestive enzymes that
breakdown organic materials outside their bodies and then absorb the dissolved nutrients
through their cell wall. This process gives off gases (formaldehyde, hexane benzene, etc.)
that can be lethal to humans. These airborne toxins are called mycotoxins. Stachybotrys
mold produces especially dangerous toxins that can cause flu-like symptoms with
headaches, hearing loss, dizziness and even bleeding in the lungs.
Moldy Facts

The British navy had more ships destroyed by fungi during the American Revolution
than what were lost in combat.

The largest living multi-cell organism is the underground portion of a single Armillaria
mushroom. In Michigan one extends more than 30 acres.

During World War II, Stalin executed several veterinarians for sabotage when the
horses under their care began to die. The horses continued to die. Execution orders
for the new crop of veterinarians were already prepared when black mold
(Stachybotrys) was found in the feed.

When the saprophyte group of fungi break down dead organisms and material, this
causes discoloration and deterioration of many furnishings and building materials.
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Bacteria
Bacteria are the most abundant living organisms on earth. They’re so small that they’re unseen
except under a microscope. Bacteria are 100 to 300 times smaller than fungi. Animal and humans
tend to be the habitat choice for bacteria. Bacteria flourish on organic food, amino acids and
moisture. Of the ten major infections that kill people, bacteria cause five.
Viruses
Viruses are extremely simple life forms and are very small. They are 100 times smaller than
bacteria. Viruses have a very simple DNA structure and have no way to multiply and grow outside
a ‘host’ cell. Only when they infiltrate living cells can they replicate.
In a sense, viruses become DNA parasites by taking over the DNA cell structure of other life forms.
But by doing this, they destroy the cells.
Domestic Arthropods
Two groups of arthropods play a big role in airborne contaminates. These are cockroaches and dust
mites. It’s not the cockroach or the mite can be dangerous themselves, but the byproducts they
produce. It’s the inhaled airborne soluble proteins, feces and debris they give off that becomes the
problem.
Dust mites absorb water from the atmosphere so they tend to next in protected areas like bedding
carpets and furniture. Since they thrive on human dead skin, they concentrate in mattresses and
pillows. There can be up to 2 million in a typical mattress. One of the problems with dust mite
feces is that it is encapsulated with a membrane, which prevents the pellets from breaking up. This
means there is a heavy build up of mite fecal pellets over time, increasing the allergen output into
the air. Here are a few likely diseases caused by indoor microorganisms:
Disease
Likely Biological Causes
1. Eye and upper respiratory irritants
(rhinitis, sinusitis and otitis)
2. Pneumonia (infection of the lower lung)
3. Asthma (inflammation of breathing
tubes)
4. Allergic alveolities (inflammation of
lower lung)
5. Humidifier disease (flu like illness with
headaches and fatigue)
6. Histophasmoisis (flue-like symptoms)
7. Alergic bronchopul-monary aspergillosis
(complicated form of asthma)
8. Dermatitis, eczema, rash (inflammation
of the skin)
9. Mycotoxicosis (inflammation of heart
caused by toxic reaction to molds)
1. Dust mites, dander, fungi & molds,
insect excretions, viruses and feathers
2. Viruses and bacteria
3. Fungi, dander, dust mites, insect
excretions and feathers
4. Bacteria, fungi & molds, feathers and
insect excretions
5. Fungi, molds and bacteria
6. Fungus in soil mixed with bird
droppings
7. Fungi, aspergillus fumigatus
8. Dust mites, dander, feathers and insect
excretions
9. Caused by specific molds.
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A special note on Humidifier Disease:
Humidifier disease is also known as humidifier lung and humidifier fever. It’s a disease of
uncertain origins. It shares symptoms with hypersensitivity pneumonitis, but with the high attack
and short term effects may indicate that toxins are involved. It’s a flue like illness marked by fever,
headache and chills. Humidifier disease has been identified with exposure to amoebae, bacteria and
fungi found in humidifier reservoirs, air conditioning systems and aquaria. The symptoms usually
start within 4 to 8 hours of exposure and end within 24 hours without long-term effects.
Organic Chemicals
Organic chemicals are widely used as ingredients in household products. Paints, varnishes and wax all
contain organic solvents as do many cleaning, disinfecting, cosmetic, degreasing and hobby products. All
of these products can release organic compounds while being used and to some degree when they are
stored.
As with other pollutants, the health effects will depend on many factors including the level of exposure and
length of time exposed. Eye and respiratory tract irritation, headaches, dizziness, visual disorder and
memory impairment are some of the immediate symptoms. Many organic compounds are suspected of
causing or are known to cause cancer in humans.
Formaldehyde
Formaldehyde is a commonly used chemical in the manufacturing of building materials and numerous
household products. It is also a by-product of combustion and other natural processes. Consequently,
substantial concentrations of formaldehyde may be present in homes.
In homes the most significant source of formaldehyde are likely to be pressed wood products such as
particle board, hardwood plywood paneling and medium density fiber wood. Other sources include
insulation products combustion by-products, paper products and miscellaneous other products. See chart
below.
Products
Use of Products
1. Pressed wood products
1. Decorative paneling, particle board, hardwood plywood
and fiberboard
2. Formaldehyde binders in fiberglass installation and foam
type insulation
3. Natural gas and oil based fumes, smoke from fireplace,
tobacco and auto emissions
4. Permanent press textiles, wood preservatives, carpet and
carpet backing, floor coverings and adhesives
2. Insulation products
3. Combustion by
products
4. Coatings, stiffeners,
water repellents and
wrinkle resisters
5. Paper products
6. Miscellaneous other
products
5. Paper towels, grocery bags, waxed paper, cosmetic
tissues and fiber sanitary products
6. Cosmetics, deodorants, shampoos, plastics, adhesives,
paints, fabric dyes, inks, disinfectants, fungicides and
fertilizers
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Formaldehyde is a colorless, pungent-smelling gas that can cause watery eyes, burning sensations in the
eyes and throat, nausea and sometimes a difficulty in breathing. High concentrations may trigger attacks in
people with asthma. There’s evidence that some people can develop sensitivity to formaldehyde. It’s also
been shown to cause cancer in animals and may cause cancer in humans.
Pesticides
EPA found in a recent survey that 75% of U.S. household used at least one pesticide product indoors during
the past year. Products used most frequently are insecticides and disinfectants. Another study found that
80% of most people’s exposure to pesticides occurs indoors and that measurable levels of up to a dozen
pesticides have been found in the air inside homes. Beyond personal use, pesticides can also enter the
home via contaminated soil or dust that floats or is tracked in from the outside, stored pesticide containers
and household surfaces that collect and then release the pesticides.
Pesticides used in and around the home include products to control insects (insecticides), termites
(termiticides), rodents (rodenticides), fungi (fungicides) and microbes (disinfectants). They are sold as
sprays, liquids, sticks, powers, crystals, balls and foggers.
In addition to the active ingredient, pesticides are also made up of ingredients that are used to carry the
active agent. These carrier agents are called ‘inerts’ because they are not toxic. Never the less, some inerts
are capable of causing health problems.
Both the active and inert ingredients in pesticides can be organic compounds; therefore, both can add to the
levels of the airborne organics. Both types of ingredients can cause the same health effects as discussed
earlier under organic compounds.
Asbestos
Asbestos is a mineral fiber that up to 1,000 times finer than human hair. It has properties that make it
resistant to chemicals, extreme heat and electrical discharges. Because of these benefits, asbestos was used
as construction material in homes as insulation, heat resistant ducting and other uses prior to 1973.
Popcorn ceilings and asbestos board siding were common uses in homes.
Asbestos was primarily abandoned in 1973 and a much safer encapsulated form was used until 1985. Its
use was completely eliminated in 1985. Asbestos is most commonly found in older homes built prior to
1973 in duct & furnace insulation material, asbestos shingles, millboard, textured paints and other coating
materials and floor tiles.
Airborne asbestos can become a problem during some action such as remodeling (cutting or sanding
asbestos-containing material, furnace removal, etc.) where asbestos material is stirred up into the breathable
air spaces. Improper attempts to remove these materials during remodeling can release asbestos fibers into
the air in homes.
The most dangerous asbestos fibers are too small to be seen but can be inhaled where they remain and
accumulate in the lungs. Asbestos can cause lung cancer, mesothelioma (a cancer of the chest and
abdominal linings) and asbestosis (irreversible lung scarring that can be fatal). Symptoms of these diseases
do not show up until many years after exposure begins.
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Lead
Lead is a soft metal element that was used as an additive in gasoline, galvanized pipes, lead lined food cans
and paints. Residential construction prior to 1930 often included lead based galvanized water pipes. This
meant that lead leached into the household water. The use of lead in pipes ceased in the early 30’s, but
homes built prior to this date could still have lead water pipes.
The greatest source of lead in homes comes from paint. Most homes built before 1950 used highly
concentrated lead in paints and varnishes. Some of the paints had up to 50% lead content. From 1950, lead
use in paint started to decline until 1978 when it was banned altogether. Homes built prior to 1950 have the
greatest risk for lead poisoning. In terms of indoor air quality, lead based paint flakes can get airborne and
get inhaled during renovation.
Lead can cause genetic mutation and cancer. Lead can be ingested or inhaled and can be carried to all parts
of the body through the bloodstream. The accumulation of lead in the body results in ‘lead poisoning.
Odor
Odor is based upon what the human nose can smell. For example molds can give off a ‘moldy’ smell,
bacteria can cause a ‘rotting’ smell, and ozone can produce a distinct ‘ozone smell’ if enough is present.
Odors come from compounds floating in the indoor air.
Sources of Home Indoor Air Pollution
There are many sources for indoor air pollution as illustrated below.
1 - Moisture
2 - Pressed Wood Furniture
3 – Humidifier
4 – Moth Repellent
5 – Dry Cleaned Goods
6 – Dust Mites
7 – Personal Care Products
8 – Air Freshener
9 – Stored Fuels
10 – Car Exhaust
11 – Paint Supplies
12 – Paneling
13 – Wood Stove
14 – Tobacco Smoke
15 – Carpet
16 – Pressed Wood Sub floor
17 – Drapes
18 - Fireplace
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19 – Household Chemicals
20 – Asbestos Floor Tiles
21 – Presses Wood Cabinets
22 – Unvented Gas Stove
23 – Asbestos Pipe Wrap
24 – Radon
25 – Unvented Clothes Dryer
26 – Pesticides
27 – Stored Hobby Products
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Pollutant Categories
For all of the previous discussions on the causes of indoor pollution, there are three broad classifications for
air contaminates: (a) Bioaerosols (microbial contaminates – bacteria, molds, viruses, etc.), (b) Volatile
Organic Compounds (fumes and gas contaminates (smoke, odors, air toxins, etc.), and (c) Particulate
Contamination (house dust, etc.).
Bioaerosols
Volatile Organic Compounds (VOC)
Particulates
Volatile Organic Compounds (VOC)
We live in a world of chemistry. Almost every physical product within our homes is based upon man-made
chemicals. The furnishings, carpets, clothing, bedding, paints, building materials, glues, soaps, cleaning
fluids, particleboard, insulation, etc. are an outgrowth of organic chemistry. Most of these chemicals are
made of petroleum-based products.
All chemicals over time tend to break down or decay. They have certain level of volatility (passing off
readily in the form of a vapor). Some chemical are more volatile than others. Organic compounds tend to
decay much faster than non-organic.
As organic materials break down, they form fumes and gasses. These gases are referred to as Volatile
Organic Compounds (VOC’s). VOC fumes and toxins part of the air we breathe. Residential indoor levels
of many volatile organic compounds tend to be especially high.
Volatile chemicals can be found in a whole range of home building materials including: roofing, siding,
framing materials, vapor sheeting, insulation, foundation sealant, sub flooring & underlayment, floor
coverings, cabinets, wall paneling, wall paper, adhesives, caulking, weather-stripping, paints, varnishes and
waxes.
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Chemical
1. Formaldehyde
2. Benzene
3. Xylenes
4. Toluene
5. Styrene
6. Toluene diisocyante
(TDI)
7. Trichiroethylene
8. Ethyl benzene
9. Methylene chloride
10. Paradichlorobenzene
11. Benzyl chloride &
benzal chloride
12. 2-Butanone (MEK)
13. Petroleum distillates
14. 4-Phenylcyclohexene
Uses in Products
1. Plywood, pressed and particle board, fiberboard,
adhesives, smoke and fumes
2. Gasoline fumes, rubber and plastic solvents, smoke,
stains, paints, varnishes
3. Adhesives, smoke, solvents, enamels, non-lead auto fuels,
wall compounds, caulking, clothes & shoe dyes, wall paper,
floor coverings, grease cleaner, varnish, pesticides and
kerosene vapors
4. Same as #3 plus vinyl floor coverings, vinyl wall
coverings and calcium silicate sheets.
5. Paints, synthetic rubber, plastics and resins
6. Paints, synthetic rubber, plastics and resins
7. Polyurethane foam aerosols
8. Solvents
9. Aerosol finishers and paint strippers
10. Room deodorizers and mothballs
11. Vinyl tiles covered with Butyl Benzyl Phthalate
12. Same as #3 (Xylenes) and #4 (Toluene)
13. Cleaning, solvent, paint thinner and stripper materials
14. Synthetic carpet and pads
VOC’s can be a carcinogen with a variety of health effects including eye and respiratory irritation and
damage, and a hazard to the heart, liver, kidneys and nervous system. They can also cause anemia and
depression.
Bioaerosols
A bioaerosol is airborne suspension of particles of biological origin (microorganisms). Bioaerosols are
estimated to be the biggest contributing source for Indoor Air Quality problems. Bioaerosols are not just
the source of annoying allergic reactions; they can also be the source of many infectious and contagious
diseases.
Bioaerosols are always present in the environment and pose no problems in most cases when the quantity
of them and the various types are kept within reasonable limits.
In order for microorganisms to release indoor bioaerosols they must get indoors, grow and multiply on
some material and then get into the air. Microorganisms can get indoors through leaky ductwork, doors,
windows, cracks in the walls or be brought in on the shoes and clothes of people entering the home. Water,
humidity, temperature, nutrients (i.e. – dirt, wood, paper, etc.), oxygen and light determine whether
microorganisms grow inside the home. The most common microorganisms found indoors are mold and
bacterial.
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Bioaerosols other than those from microorganisms (i.e. – pollen, dander) get indoors in the same way as the
microorganisms. These do not multiply but may become a problem if they accumulate.
Refer to the previous section on biological contamination for more information.
Particle Pollutants
House dust comes with living indoors. If we took a scraping of house dust from central air filter and put it
under the microscope, we’d see dead skin, animal and human dander, animal and human hair, insect parts,
insect & dust mite fecal pellets, paint flakes, building material particles, furniture fibers, clothing fibers,
carpet fibers, etc. The list goes on and on. The house dust collected on the filter reflects airborne particles
that were big enough to be captured in the filter.
Particles are very small substances that are light enough to float suspended in air. Examples are mists, dust
or pollen. Small, invisible particles can penetrate deep into the lungs where they may stay a long time and
may cause acute or chronic respiratory problems. Larger particles such as some molds, pollen, animal
dander, and dust allergens do not penetrate as deeply but may cause an allergic reaction.
Health effects can range from irritation of the eyes and/or respiratory system to more serious effects such as
cancer or decreased lung capacity. Biological particles such as animal and insect allergens, viruses,
bacteria and molds can cause allergic reactions, infectious diseases and can produce toxic products, which
may be released into the air.
Indoor Air Solutions
There are 3 basic means to improve indoor air quality: (a) Eliminate (Source Control), (b) Ventilate
(Dilution), and (c) Clean the Air (Filtration).
Source Control
Source control eliminates or controls the source of pollution. This is a fairly broad subject that goes
beyond.
Equipment Cleaning
Mold thrives in a dirty moist environment. If dirt collects on the indoor coil, this becomes a perfect place
for mold to grow. The indoor coil is located downstream from the system filter so mold byproducts flow
freely into the home. Dirt that accumulates in the equipment can cause this same condition. A dirty coil or
an accumulation within the equipment should be cleaned to help avoid indoor air problems.
Duct Cleaning
Dirt can collect inside duct as well and can be a source of indoor air pollution. Cleaning dirty ductwork
may help correct the situation. The big question is how did the duct get dirty in the first place. If the
ductwork leaks, it allows dirt to enter the system. Cleaning the duct may only be a temporary solution
unless the duct is sealed at the same time.
Most ducts in homes are made of one of three materials: sheet metal (rectangular or round), duct board or
flex duct. Sheet metal ducts are sometimes lined on the inside with fiberglass or other material to insulate
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the duct. Sometimes they are un-insulated, or insulated on the outside with only bare metal exposed to the
air passing through. The cleaning method used to clean the duct varies by the type of material used.
Duct cleaning equipment should include HEPA filtration to prevent debris from entering the home in the
cleaning process. The National Air Duct Cleaning Association (NADA) has set duct-cleaning standards for
the industry.
Seal Leaky Duct
Homes with forced air heating or cooling systems almost always have leaky ducts. On the average, up to
25% of the air treated by the indoor equipment never reaches any of the rooms. Over 90% of homes have
some type of air duct leakage.
When the blower operates in a system with leaky supply ducts, air leaks out causing a pressure drop inside
the home due to the loss of air. As air is pushed into basement, garage, crawlspace or attic, outside air is
sucked into the lower inside pressure through attic, wall and floor cracks. This outside air carries pollutants
such as mold and pollen into the home. It brings in humidity as well. This puts an additional load on the
heating/cooling equipment and also causes indoor air pollution problems.
Leaky return air ducts cause a couple of problems.
1. Leaky return air ducts suck in air from the outside when the blower runs. This pulls in
outside air into the ductwork. The outside air carries pollutants into the ductwork, through
the filter, through the indoor coil and on into the home.
2. If the home has an equipment room with a negative pressure, this can affect combustion on
gas furnaces & hot water heaters. This can also cause flu gases to back draft out of the
vent into the home. Anything that affects combustion also causes the formation of carbon
monoxide. This can be a very dangerous situation.
Leaky ducts also create capacity and efficiency problems for heating and cooling equipment. For example,
if 10% of the return air comes from a 120 degree attic with an 85% dew point, 75 degree return air gets
warmed up to 79.5 degrees (with much greater humidity) by the attic air before it reaches the coil. A 12
SEER unit only performs like a 9.6 SEER unit. A 3-ton unit only delivers 2.1 tons of cooling.
Many homes use wall and joist cavities as return air ducts. If not installed properly, these can leak to
unconditioned attics or crawlspaces.
Sealing leaky ducts is another example of source control.
Poor Air Distribution in Ductwork
A lack of return air can cause the home or part of the home to experience negative pressure. This is
particularly true if the home has a central return. Homes with central returns often have their infiltration
rates double or triple when interior doors are closed and the blower is on. The main body of the home goes
into a negative pressure when doors are shut to other parts of the home. This causes warm, humid air to
enter the home. This added moisture causes humidity levels to increase and contributes to the formation of
mold.
In the north during the winter, bedroom pressurization forces warm moist air through any vapor barrier
openings and moisture flows into the walls or attic. This leads to condensation and mold problems. This
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can also be a problem in the south when a cold front passes through. However, southern climates have an
additional problem in the summer.
CFM usually drops to the bedroom when the door is shut, thus decreasing comfort as well. Ideally each
room should have its own return air where allowed (i.e. – bathrooms, laundry rooms, kitchens, etc. should
not have return airs. Installing ‘jump duct’ and ‘transfer grilles’ are ways of providing pressure relief
without installing a separate return air duct to the room.
Undersized duct systems create problems as well by dramatically increasing the air velocity in the system.
The velocity of air going across the indoor coil is one of the factors that effects dehumidification in the
cooling season.

Undersized duct affects the indoor coil’s ability to dehumidify.

Undersized duct increases noise level through the system due to the increased air velocity.

Undersized duct causes a lower negative pressure at the blower, which causes dirt and debris
to be sucked through the filter.

Undersized duct reduces the airflow to rooms through out the house. Rooms far from the
unit are starved for air. This creates hot or cold spots in the home.
Moisture Control – Too Much
The occupants within the home produce tremendous amounts of water vapor each day. The following chart
shows the volume of humidity in the air produced by various household tasks. .
Activity
Cooking (3 meals a day)
Dishwashing (3 meals a day)
Bathing (0.2 liter per shower)
(0.05 liter per bath)
Washing Clothes
Drying Clothes
Cleaning Floors
Normal Breathing and Perspiration
Total Volume of Humidity per Week
Liters/Week
6.3
3.2
2.4
1.8
10.0
1.3
38.0
63.0 Liters
As mentioned previously, microorganisms need moisture to live and reproduce. If the relative humidity in
the home is over 70%, materials containing carbon may absorb enough moisture to support microbial
growth. Dust mites can survive in conditions over 50% relative humidity. Reducing humidity in the home
is the single most effective control for dust mites; they thrive in moist air. People are most comfortable in a
relative humidity range between 35% and 55%. For homeowner comfort levels of 40% to 60% are
generally recommended, although a range of 40% to 50% is ideal to prevent biological growth.
Over sizing air conditioning equipment can create conditions where the relative humidity can rise above
this 50% recommendation. An oversized air conditioner drops the sensible temperature down quickly to
shorten the run time. The shorter run time does not allow sufficient time for the air conditioning system to
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take out the latent heat and dehumidify the home. Humidity levels will rise and this can cause a clammy
‘cave’ like feeling that’s uncomfortable. It also provides molds with the moisture to grow and flourish.
Correct sizing is crucial to humidity control, particularly if you live in a humid climate.
An oversized unit also tends to cycle off and on more frequently that a unit that is properly sized for the
home. This creates additional problems. Whenever the HVAC system and blower shuts down, high
pressure at the registers rushes to low pressure at the blower thus creating an instant blow back. The
convection current causes air to continue moving up and down the supply duct reintroducing contamination
to the coil from the home. This condition contributes to the possible build up of biological contaminates at
the coil.
It’s important to do load calculations, particularly with figuring the cooling load in warn, humid climates.
Bigger is not better.
Homeowners generally want high efficiency equipment to lower cooling costs in the summer. This can be
a double edge sword in humid climates if you are not careful in matching the coil to the condensing unit.
Generally the higher the efficiency of the match up, the higher the coil temperature is. Coil temperature is
one of the major factors in the coil’s ability to dehumidify. This is expressed in what’s called the ‘ST’
ratio. The higher the ST ratio of the coil and condensing unit match up, the less dehumidification that can
occur and the higher the relativity humidity within the home. Some match ups can achieve an ST ratio of
1, which means no dehumidification is occurring at all. The irony in this is that many homeowners will
feel uncomfortable at this higher humidity and will lower the thermostat to a lower setting. It’s estimated
that for every degree Fahrenheit drop in temperature causes a 10% increase in cooling costs. Dropping the
temperature 3 degrees at the thermostat can wipe out the predicted energy savings. The contractor must be
careful in matching the evaporator coil to the condensing unit, particularly in humid climate.
Some equipment used time delay relays on cooling applications to keep the indoor blower operating after
the end of the cooling cycle. In some cases it was used to get some residual cooling to increase the SEER
rating. In other cases it was done on poorly designed blower/coils to dry out the coil before the next on
cycle to prevent water from blowing out. The typical coil holds between .25 and .50 gallons of water when
the compressor shuts down. The longer the blower runs, the more moisture gets re-evaporated. This is
especially true under short cycle conditions when almost all of the condensed water gets re-evaporated into
the home. This again causes the humidity level to rise within the home. Do not use time-delays on cooling
applications.
As mentioned before, any condition that causes the home or part of the home to be at a negative pressure
will cause outside air to enter the home. This will introduce humidity into the home and will cause the
humidity level to increase.
The air conditioning does remove moisture from the home while it’s operating. However, it does not run
very often in the fall or summer. Some southern climates can even have humidity problems in the winter.
Depending on the local climate and the type of building materials used in the home (the tightness of the
home) there may be need for dehumidification year round to ensure a healthy home. Whole house
dehumidification products are available to solve this type of problem.
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Moisture Control - Lack of humidity
Most people tend to be most comfortable at humidity levels ranging from 35% to 55%. Low relative
humidity adversely affects the home, furnishings and the occupants. Dry indoor air will rob moisture from
people, plants and furnishings. This can cause chapped skin & lips, scratchy nose and throat and the
discomfort of static electricity.
Dry air can damage furnishings by stealing moisture. For example, when the relative humidity of air is
60% a thirty-pound chunk of wood holds over three pints of water. At 10% relative humidity, the wood
will not hold one pint of water. At the lower moisture content, the fibers of the wood shrink. This places
internal stresses on the wood and causes it to crack and break.
Humidifiers are available to add moisture to the indoor air to increase humidity levels. Studies by the EPA
have shown that ultrasonic and impeller (cool mist) types of humidifiers can disperse microorganisms from
their water tanks into indoor air. Ultrasonic and impeller types of humidifiers can also disperse minerals
from the tap water that forms ‘white’ dust in the home. Evaporative and steam evaporative types of
humidifiers generally disperse less if any of these pollutants into the air.
Humidifiers pose a different problem in colder weather during the winter. Depending on the types of
windows used in the home, condensation may form on the windows. For example, with indoor air relative
humidity at 48%, standard window glass with an R-2 rating has a dew point of 40 degrees. Condensation
will form on the window when the outside temperature drops to 0 degrees. The condensation will get
heavier as the outside temperature gets colder. There are a number of solutions to this problem including:





Setting the humidistat to a lower temperature.
Using a humidifier and humidistat that automatically adjust for falling outdoor
temperatures.
Operating a ventilation system to decrease the relative humidity. Even a small bathroom
fan will decrease the humidity.
Putting tight fit plastic over the interior surface of the windows to raise the surface
temperature.
Replacing the windows with ones with a higher R-value.
Evaporative Coolers
Evaporative Coolers are used in dry climates as a means of cooling the home. An evaporative cooler takes
dry outside air and passes it through a wet media. In the process moisture evaporates and the air is
consequently cooled. This condition air is routed into the home. Window is usually left open to relieve the
pressure from within the home.
The reservoir that holds water in an evaporative cooler and the wet media are breeding grounds for
microorganisms. Fortunately the exchange of air going in and out of the home prevents the buildup of
indoor contaminants. However, if microorganisms grow within the evaporative cooler, the spores and
toxins they produce will circulate through the home.
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Home Construction
Home construction practices may allow air to circulate from the home into the attic through wall cavities or
through opening around recessed lights, registers, grilles, etc. This air contains moisture in the form of
water vapor that was created in the kitchens, bath and other places in the home. This moisture will
condense when it hits a colder surface such as roof sheathing where it can damage the wood. Sometimes
the roof damage is mistaken as being caused by a leak when the real problem is air & water vapor leakage
from the home into the attic.
Sealing all entry points from the home into the attic or walls prevents moisture from entering.
Peeling paint is an example of a problem caused by water vapor traveling to the inside of the walls where it
condenses.
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Water Leaks
Microbes can multiply within a short time after water leaks into the home. Water-damaged ceiling tiles,
sheetrock, wall coverings, wicker ware and wood are good places for microorganisms to grow. They also
can grow on water-damaged chair fabric, furniture and in carpets. Water-damaged materials can support
microbial growth long after they appear to be dry. Water within the home also causes high relative
humidity.
Common causes of water leaks include improper landscaping, roofing problems, flashing around windows
and doors, etc.
Living Habits
The federal government recommends homes be weatherized in order to reduce the amount of energy
needed for heating and cooling. However, steps should also be taken to minimize the sources of pollution
from within the home. Weatherization does not cause indoor air problems (with the exception of some
caulks). However, measures to tighten the home can reduce the amount of outdoor air infiltrating into a
home and concentrations of indoor air pollutants from sources within the home can increase. Depending on
the living habits, this may necessitate the need for ventilation.
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People have a lot of influence on the creation and control of pollutants within the home. When using
cleaners and other products that can emit gases, the manufacturer’s written instructions on the use of the
product should always be followed. When doing activities such as painting or hobby work, the room
should be ventilated by opening windows. A little common sense goes a long ways to prevent the build up
of VOC contaminants.
Cleaning the Air
Filtration
System filters for heating and air conditioning systems only deal with one type of particle, house dust.
These conventional filters prevent large particles of dust and debris from collecting on components such as
motors, the heat exchanger surface and the indoor air coil surface where they could damage the equipment.
Dust collecting around motors can cause the motor to overheat and fail. Dust can also collect on bearings,
which can interfere with lubrication of motor parts that can cause the motor to failure.
Dust collecting on the surface of heat exchangers can cause hot spots as the dust burns off when the
furnace starts. These hot spots can form holes in the heat exchanger, which allows combustion byproducts
to enter the home.
Dust collecting on the inner surface of the indoor coil interferes with the airflow passing through the coil,
which interferes with heat transfer. This lack of heat transfer causes several problems to an air conditioning
system: (a) The system does not cool effectively, (b) The refrigerant may exit the coil as a liquid, which can
damage the compressor and cause failure, (c) The dust on the coil is an excellent breeding ground for molds
and fungi, which contribute to IAQ problems. On heat pump systems a dirty indoor coil will also cause high
head pressure problems that can also cause compressor failure.
Note- The system filter must be changed frequently to prevent an accumulation of dirt. Clogged filters
interfere with airflow to the unit. This condition causes the same affect as a dirty indoor coil mentioned
above. It also creates a couple of more problems. As negative pressure builds up at the blower, dirt is
sucked through the filter, which causes all the problems mentioned in the previous paragraph. The lack of
airflow to the unit in the heating season can also cause the furnace to overheat. This can cause the limit
control to cycle off & on and could eventually cause the heat exchanger to fail.
Dust is visible. We cannot see the smorgasbord of inhaled particles including fungi and mold spores,
pollen grains, bacterial, viruses, bacteria, animal and insect debris & fecal material, fumes, smoke and
more. They all range from .05 micron to 30 microns in size.
A standard mechanical filter is effective at capturing particles larger than about 50 microns. Thus the real
indoor contaminants (germs, fumes, toxins) pass right through a convention system filter and circulate
through the home. It’s the tiniest particles that make up 99% of the debris in the air circulating in the
home.
The common measurement for particles is in microns. It’s an extremely small unit of measurement. One
micron is 0.000001 of a meter. Putting this in perspective, one inch equals 25,400 microns. Here is a
comparison of particle size in microns.
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When talking about filters it’s important to understand how they are tested and rated. This can be
confusing to consumers who do not know the difference in the way the tests are conducted.
Weight Arrestance Test
This measures the percent of weight of the debris collected by the filter. Thus a 95% rated filter can collect
95% of the debris in terms of weight alone. It has no bearing on the size of the particles and is only a
reflection of the filter’s ability to capture large particles of lint and dust. Considering that most of the harmful
pollutants are less than 2 microns in size, this type of rating is really very meaningless when it comes to
Indoor Air Quality.
Atmospheric Dust Spot Test
This was used to rate air cleaner efficiency (both filters and electronic air cleaners). The removal rate is
based on the filters ability to reduce soiling of a clean paper target. The rating is expressed as percentage of
1 to 100. Once again this test does not consider particle size.
MERV Rating
The American Society of Heating and Air Conditioning Engineers (ASHRAE) and the air filtration industry
have come up with a standardized rating system that considers particle size in testing. This is called the
Minimum Efficiency Reporting Value (MERV) and describes the filter’s ability to capture all size particles.
This rating tests the ability of the filter to capture particles ranging from 0.3 to 10 microns. The test covers
three bands of 0.3 to 1.0 microns, 1.0 to 3 microns and 3.0 to 10 microns. The higher the MERV rating, the
better the filter is at capturing small particles.
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The following chart gives more information on the MERV ratings.
Group
Number
1
2
3
4
Average
Particle
Size
0.3 - 1.0
Micron
Average
Particle
Size
1.0 – 3.0
Micron
Average
Particle
Size
3.0 - 1.0
Micron
Average
Arrestance
Minimum
Final
Resistance
(in W.G)
MERV 1
-
-
Less than
20%
Less than
65%
0.3”
MERV 2
-
-
Less than
20%
65 – 69.9%
0.3”
MERV 3
-
-
Less than
20%
70 – 74.9%
0.3”
MERV 4
-
-
Less than
20%
75% or
greater
0.3”
MERV 5
-
-
20 – 34.9%
-
0.6”
MERV 6
-
-
35 – 49.9%
-
0.6”
MERV 7
-
-
50 – 69.9%
-
0.6”
MERV 8
-
-
70 – 84.9%
-
0.6”
MERV 9
-
Less than
50%
85% or
greater
-
1.0”
MERV 10
-
50 to 64.9%
85% or
greater
-
1.0”
MERV 11
-
65 to 79.9%
85% or
greater
-
1.0”
MERV 12
-
80 to 89.9%
90% or
greater
-
1.0”
MERV 13
Less than 75%
90% or
greater
90% or
greater
-
1.4”
MERV 14
75 to 84.9%
90% or
greater
90% or
greater
-
1.4”
MERV 15
85 to 94.9%
90% or
greater
90% or
greater
-
1.4”
MERV 16
95% or greater
90% or
greater
90% or
greater
-
1.4”
MERV
Rating
While talking about filtration, the indoor equipment coil on higher efficiency match ups can create a
problem for systems with regular filters. Standard hoarse hair or foam filters have a MERV rating of 1. A
wet high efficiency coil with many fins per inch can have an effective filtration efficiency of up to MERV
6. This means that particles that pass through the filter can collect on the coil, thus creating ideal
conditions for biological contamination. The secondary heat exchanger on a 90% gas furnace also serves
as a filter to collect dirt. In order to protect high efficiency equipment, a filter with at least a MERV 6
rating is required.
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Germicidal Lamps (UV Lights)
Even filters with good MERV ratings will not be able to collect every thing out of the air. Consider the
size of viruses, bacteria and mold.
Viruses
.022 - .3 micron
Bacteria
.20 – 1.25 micron
Mold Spores
1.5 – 20 micron
Germicidal lamps kill these organisms. These lamps generate a UV light. When UV light hits a microbe
cell and will damage its DNA. The smaller the organism, the less time needed for the kill.
Filters are generally not designed to remove gaseous pollutants. Beyond killing microorganisms, some UV
lights can also eliminate some odors. Smoke, fumes and vapors are some combination of organic
compounds in a gaseous state. UV lights break these compounds down to eliminate the odor.
Ozone Generators
Ozone generators have also been promoted as a cure for indoor air quality problems. Ozone is a highly
reactive gas. The theory is that ozone gas will react with harmful airborne gases and convert them to
harmless substances. According to EPA the ozone levels necessary to kill microbiological organisms such
as mold spores is five to ten times the approved levels for humans. Ozone can cause lung damage and EPA
strongly discourages the use of such devices. Refer to the EPA website www.epa.com and refer to the
article on “Ozone Generators that are Sold as Air Cleaners: An Assessment of Effectiveness and Health
Consequences” for more information on this subject.
Ventilation
An older home that has not been weatherized can expect one complete air change per hour through
infiltration. An air exchange refers to the length of time it takes to replace the entire air volume within the
home. A very loosely constructed house could experience as many as 2-1/2 complete air exchanges each
hour. With this amount of infiltration there is little chance of build up of internal pollutants. However, this
amount of infiltration increases the chances of pollutants such as pollens from being carried in from outside
and higher heating and cooling costs to condition the air.
Over the last 40 years home construction practices have continually improved to minimize the amount of
natural infiltration in order to lower heating and air conditioning costs. Older homes have been
weatherized as well. These construction practices have tightened up homes considerable, which
consequently have caused indoor air pollutants to build up.
As mentioned previously in this article, conditions like leaky ducts can cause a home to have negative
indoor pressure. This can affect the combustion process in gas appliances such as hot water heaters, which
can be dangerous to the people living in the home. Negative pressure can also draw outdoor air pollutants
into the home.
Ventilation is the cure for these conditions. The act of introducing outside air into the conditioned space or
of removing stale air from the space is termed ventilation. If a home is built tight, it must be ventilated
right. Unlike infiltration, which brings in an uncontrolled amount of air from outside the home that
introduces pollutants and humidity, ventilation controls the introduction of fresh outside air to the heating
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and air conditioning equipment where it is treated before it enters the home. A constant supply of fresh air
creates a slight positive pressure in the home, which counteracts infiltration. This reduces pollutants from
infiltrating the home and also helps prevent drafts from within the home. The positive pressure also helps
avoid combustion problems on gas appliances.
The ventilation system should be sized so each person in the home has a minimum of 15 cubic feet per
minute (CFM). This ventilation rate should be continuous while the home is occupied. The higher the rate
of ventilation, the more important it is to recover heat and energy from the outgoing air. A heat or energy
recovery unit is a devise capable of transferring heat and sometimes moisture between two airstreams.
For many years contractors and manufacturers have recognized the need to introduce outside air into the
home to provide a total comfort environment. Prior to the 70’s it was a simple process of running a fresh
air intake directly to the return air duct or plenum. This practice was discouraged over time because of the
increased energy costs in treating this unconditioned air.
Today whole-house ventilation can be provided by heat or energy recovery ventilators (HRVs or ERVs).
Both reduce indoor air pollution be exhausting stale, contaminated air and introducing fresh air from
outside.
An HRV is a combination of fans, controls, and heat recovery elements that exhaust stale air from the
home, bring fresh air in from outdoors and transfers heat energy from one airstream to the other. HRVs are
usually recommended for colder climates with longer heating seasons.
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1. One set of ducts collects stale air from the kitchen, laundry and bathrooms. This
stale air passes through the HRV and is exhausted out side.
2. The other ducting system draws in fresh clean air from outdoors through the
HRV unit.
3. As the two air streams pass each other, heat is transferred from the outgoing stale
air to the fresh incoming air. There is no mixing of air streams.
4. The HRV unit is able to capture up to 85% of the energy from the outgoing stale
air.
An ERV functions similarly to an HRV. An ERV is capable of reducing the moisture content of the fresh
incoming air as well. As a result, they can reduce the latent load on the air conditioning system during
summer operation. ERVs are preferred for warmer, humid climates with longer cooling seasons. For
successful winter operation, ERVs must be equipped with a suitable defrost mechanism.
Other Conditions Affecting Indoor Air Quality
Dirt Sock Syndrome
The indoor coil in heat pumps is used for both cooling and heating. In a heat pump system, the coil
generates high levels of moisture in both the heating and cooling cycles. Everyone knows the coil
condenses moisture while in cooling. But the coil can also collects moisture at high temperature levels in
the heating cycle. When the coil heats up during the heating cycle, the moisture on the fins evaporates.
This causes any mold on the coil surface to dry out and go into hibernation. As soon as the heating demand
is satisfied, moisture immediately starts condensing on the coil. This warm, moist condition is ideal for
explosive growth of any molds hibernating on the coil.
Molds growing on the indoor coil of heat pump systems are responsible for ‘dirty sock syndrome’. The
odor given off the molds is describes as smelling like dirty socks.
Attic fans
Most powered attic fans unintentionally suck conditioned air out of the home below through leaks in the
ceiling and attic floor. 200 to 400 CFM is common. This again causes a negative pressure within the home
and outdoor air is sucked in as a result. This sucks pollutants into the home as well as humidity. This
contributes to indoor air contamination and the increased air conditioning load is often more than a ton of
sensible and latent heat.
A powered attic fan can also cause back drafting of appliances in the attics. Some construction practices
put the hot water heater in the attic.
Crawl Space Ventilation
Crawl space vents often do more harm than good. Outside air is usually too humid to dry anything out
through most of the year. Instead it makes things wetter. Each 1,000 square feet of apparently dry soil
contributes 100 pounds (12.2 gallons) of water per day to the house. In contrast, all the bathing, cooking
and breathing of a typical family of four equals about 8 gallons a day.
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Crawlspaces should be treated like min-basements with good exterior drainage and insulation installed at
the perimeter rather than in between floor joists. Crawlspaces should be sealed to make them airtight. The
crawl space should be sealed with a vapor barrier as well.
Basement Moisture
Basement water problems are common across North America. A damp and musty basement in not only
unpleasant, it can also be unhealthy. Moisture travels from the outside of homes into the basement by one
of four means.
1. Ground water. This is actual water that seeps into the basement. Liquid water can enter
from windows, doors, foundation walls and outside flashing details. Soils, landscaping and
waterproofing all play key roles in foundation leakage issues.
2. Capillary action. This is water whickering up through the slab or up foundation walls from
damp or wet footings.
3. Vapor diffusion. This is the movement of water vapor between two areas of different vapor
pressure.
Construction Practices - Vapor Barriers
It’s estimated that 60% or more of moisture problems in the home are caused by a failure in the exterior of
the home. Heat goes from warm to cold and water vapor flows from wet to dry. If areas of a home are left
uninsulated, they will get colder and the relative humidity will be higher. Thus, a corner of a ceiling that
has no insulation attracts moisture and mold problems can occur in that corner. If walls are insulated, but
there are gaps that are not insulated, moisture builds up and mold can develop. Insulation needs to be
installed correctly to avoid this type of problem.
In colder climates construction practices often put a vapor barrier on the inside of exterior walls to prevent
vapor diffusion, the flow of water vapor. The vapor barrier prevents the flow of moisture from the home to
the outside during the winter. Otherwise the moisture will condense in the walls and in the attic as it flows
to the outside of the home. This can cause mold and rot. The moisture can also freeze in the insulation
where it loses some of its R-value, thus causing more heat loss from the home.
However there is a problem in the summer with putting a vapor barrier on the inside of exterior walls in
humid climates. Water vapor flows from the hot humid air to the cooler, drier air inside the home. If a
vapor barrier is installed on the inside walls, water vapor will condense within the exterior walls during the
summer.
A polyethylene vapor barrier works fine for the heating season but not for the cooling season. A
polyethylene vapor barrier can trap moisture in walls and cause mold problems Wall systems should be as
tight as possible, but make the insulation breathable. Some building contractors use a house wrap on the
outside of the building that has about 58% permeability. It serves as an air barrier from the outside but
allows water vapor from the inside to evaporate out.
Because of the vapor diffusion issues in the air conditioning season, the vapor barrier should be installed on
the outside walls or not at all in southern climates. When a vapor barrier is not used, this is called a
breathable wall. Another consideration for southern climates is the type of wallpaper used on outside
walls. Vinyl wallpaper acts as a vapor barrier and should not be installed on perimeter walls.
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Construction Practices – Thermal Bridging
Thermal bridges are areas of the building where adjoining materials have different rates of conductivity.
Besides leading to increased energy demand, the higher heat flow through thermal bridges lowers the
surface temperature where condensation can form. This is a potential growth problem for microorganisms
such as mold.
Thermal bridging often occurs in external walls when the cavities are closed with materials of poor
insulating quality. Such thermal bridging produces problems of condensation, pattern staining and mold
growth around these openings.
Heat loss paths around a typical
Window opening
IAQ Industry Trends and Opportunities
Here’s an overview of the United States population that have allergy, sinusitis or asthma problems.
25%
Of people have allergies
12.5 %
Of people have sinusitis
10%
Of people have asthma
Considering the U.S. 2000 census puts the population at 281.4 million, these statistics indicate there are a
lot of households that have an immediate need for services, which reduce allergens and other sources of
indoor air pollution. There are over 100 million people suffering from allergies, asthma and sinusitis. Of
these, 60% do not know how to treat the indoor air problem other than treating the symptoms with
prescriptions or over the counter drugs.
The current IAQ market size is estimated to be between 2 and 5 billion dollars for both residential and
commercial products and is expected to $12 billion a year by 2012. Indoor Air Quality is big and is going
to get much bigger.
Only a few years ago most contractors thought about Indoor Air Quality primarily in terms of duct
cleaning. Contractors did sell IAQ components such as filtration devises and humidifiers, but tended to
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treat these as accessory sales. With the growing awareness of indoor air health problems and the
introduction of new technology, IAQ is quickly becoming an industry onto itself.
Consumer research shows that most homeowners do not know the solution to poor indoor air quality. Look
at the popularity of portable air cleaners. They are advertised on television and in print. You see them in
stores such as Office Depot, Home Depot, etc. Yet the Mayo Clinic has found out that air cleaners attached
to whole house systems work better than free-standing air cleaners. As consumers become aware of the
capability of whole house system solutions to improve indoor air, there will be a growing demand for these
products.
Another sales benefit of these IAQ products is that they’re tax deductible if prescribed by a doctor,
There are some excellent tools available that can test Indoor Air Quality within the home, such as the
AirAdvice System. Such tools lend themselves to diagnostics and can be a great marketing & sales aid.
Future articles on this website will focus on the marketing and sales aspects of Indoor Air Quality.
The question now becomes how will you pursue IAQ opportunities? Perhaps you only want to sell certain
accessories such as humidifiers and air cleaners, and do not want to get into sealing ductwork. That’s fine.
In that case, be careful in what your sales people promise consumers. For example, the best air cleaning
devise in the world will do little good in the home if the ductwork leaks.
Remember that a house is much more than four walls and a roof. It is an interactive system made up of
many components. Each component influences the performance of the entire home. The more knowledge
you can attain on how these components affect indoor air quality, the better you’ll be positioned to provide
comfort solutions to your customers.
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Why Is This Important To You?
Having a good understanding of indoor air quality fundamentals:

Provides you with the knowledge to see how indoor air quality affects health.

Provides you with the knowledge to know what causes indoor air quality problems.

Allows you to know how design and installation practices affect indoor air quality.

Introduces you to possible solutions to improve poor indoor air quality.

Provides you with the knowledge to advise your customers on IAQ issues. Knowledge
builds confidence and credibility.
Indoor Air Quality is a growing industry with a huge potential. IAQ products and services
can provide profitable revenue growth for your company.
Customers expect contractors to solve all of their comfort needs including
Indoor Air Quality. How knowledgeable are you and your employees on this
subject?
Do you understand how you’re your present design and
installation practices affect Indoor Air Quality?
Do you know where and how microorganisms grow and
flourish within a heating/cooling system? Do you know how
to prevent them from forming?
Do you understand how relative humidity affects
microorganism growth and how to control humidity levels in
the home?
Do you know why VOC’s concentrate in today’s home and
how to prevent this from happening?
Do you understand how source control, filtration and
ventilation improve Indoor Air Quality?
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