GAS HEATING
Planned Maintenance
Produced by
Joe Marchese
Personal Safety




Good safety practices will prevent
many injures
Safety must be first on your mind at all
times
Always remove loose items when
working around equipment with moving
or rotating parts
Be cautious of sharp objects
Personal Safety




Always lift with your legs and not with
your back
Wear a back support belt when lifting
heavy objects
When working with electrical equipment
always verify that the power is off
Do not rely on a shut-off switch or
disconnect being off -- always check
yourself
Personal Safety





Be cautious of hot surfaces or work
areas
Be cautious of any gas or oil leaks
Always check for carbon monoxide
Always follow proper safety practices
when working with ladders
Be cautious of confined spaces provide proper ventilation when
required
Personal Safety Equipment
Safety Shoes
Safety Goggles
Gloves
Pocket Voltage Detector
Back Support Belt
Oil Absorbent
Personal CO Detector
Why Perform
Planned Maintenance?




To reduce equipment failures
To keep equipment operating in a
safe manner
To keep equipment performing at
peak efficiencies
To maintain good indoor air quality
What is the most important
concern for a service
technician while performing
a preventive maintenance
inspection?
SAFETY
Safety




Carbon monoxide poisoning is a major
concern
Natural gas leaks can create a serious
hazard
Fire as a result of damaged or
bypassed safety controls
Lack of heat from improperly operating
furnaces
Keeping Equipment
at Peak Efficiency



Poor electrical connections can cause
the system to work harder
Improper gas combustion will
decrease the efficiency of a gas-fired
furnace
Dirty filters will reduce the airflow
through a system which will decrease
the system’s efficiencies
Indoor Air Quality



Humidifiers that are not operating
properly can lead to poor indoor air
quality
Filters not maintained can lead to poor
indoor air quality
Carbon monoxide leaking into a
structure is a serious indoor air quality
issue
How Long Should a
PM Inspection Take?

Depends on:
– the type of equipment
– the detail in which the inspection is
performed
SHORT INSPECTION vs. LONG INSPECTION
What Are the
Most Important Tools
Used on a PM Inspection?
Your hands
Your eyes
Your ears
Your nose
First Steps

Determine the type of furnace
– Barometric - standing pilot
– Barometric - direct spark Ignition
– Induced draft - DSI or hot surface
ignition
– High efficiency - sealed combustion
Maintenance Task Items


Always following the equipment
manufacturer’s guidelines
Tasks can be grouped into four major
categories:
–
–
–
–
Inspection
Cleaning
Lubrication
Operation checks
Maintenance Task Items




Check availability of combustion air
(80% furnaces only)
Clean and inspect air system
accessories such as humidifiers and
electronic air cleaners
Check the condition of the electrical
wiring and tightness of the terminals
and connectors
Clean or replace air filters
Maintenance Task Items




Clean and inspect fan compartment
Clean and inspect the condensate
drain system
(90% furnaces only)
Clean and inspect the vent system
Clean and inspect burners and heat
exchanger
Maintenance Task Items






Check thermostat and heat
anticipator or cycle switch settings
Check sequence of operation
Check pilot/burner operation
Perform combustion tests
Check temperature rise
Check safety controls
Combustion Air



Different furnace designs will have
different styles to bring combustion air
into a furnace.
An 80% efficient furnace normally uses
the air surrounding the furnace for its
combustion air
A 90% plus furnace normally uses
outside air for its combustion air
Combustion Air


When performing an inspection the
location of the furnace should be
examined to make sure it has a
sufficient volume to provide enough
combustion air
Make sure no other gas-fired
appliances (such as a dryer or hot
water heater) steal combustion air
from the furnace
Combustion Air


Verify that the combustion air will not
be contaminated by halogen
compounds, such as fluoride,
chloride, bromide and iodide vapor.
If installed in a laundry room, make
sure the exhausted products vented
by the dryer do not enter the furnace
and are used for combustion air
Unconfined Space


An unconfined spaced has a volume of
at least 50 cubic feet per 1000 Btus
input total for all appliances located in
the space
If the unconfined space is constructed
unusually tight, the combustion air must
come from outside air or from spaces
freely communicating with the outdoors
Confined Spaces


A confined space has a volume less
than 50 cubic feet per foot per
1000 Btus of total input rating of all
appliances installed in that space
There must be provisions for supplying
combustion air; it can be ducted in from
outdoors or from an unconfined space
Confined Spaces
The number of
openings and the
size of the openings
will depend on
whether the air
comes from the
outside or from
adjoining
unconfined space
Combustion Air Requirements

If combustion air is brought from
within the structure there must be 2
openings
– Each opening must have a minimum
free area of not less than 1 square inch
per 1000 Btu of total input rating for all
gas appliances in the space (should
not be less than 100 square inches)

If construction is unusually tight,
outside air must be brought in
Combustion Air Requirements

If combustion air is brought from
outside the structure there must also be
2 openings, however:
– If two vertical ducts are used they must
have at least 1 square inch of free area
per 4000 Btus of total input for all gas
appliances
– If two horizontal ducts are used they must
have at least 1 square inch of free area
per 2000 Btus of total input for all gas
appliances
Combustion Air Requirements


A single opening can be used if it
has a free area of 1 square inch per
3000 Btus of total input for all gas
appliances
Failure to comply with these
guidelines may result in a furnace
starved for combustion air which
could lead to the formation of carbon
monoxide
Cleaning and Inspecting
Air System Accessories
Humidifiers
Maintenance required:


Replace media pad
Clean mineral deposits from:
– water reservoir or drain pan
– float, float valve orifice, and valve
seat
– water solenoid valve orifice and
strainer
Humidifiers
Maintenance required:



Check for water overflow
On wheel-type humidifiers, an
approved water treatment solvent can
be applied to water reservoir
If a bypass humidifier is used, make
sure the dampers are open for winter
operation
Recommended Indoor
Humidity Levels at
Various Outdoor Temperatures
AT OUTDOOR
TEMPERATURE
(F)
RECOMMENDED
INDOOR RH
(%)
-20
15
-10
20
0
25
10
30
20
35
30
40
Electronic Air Cleaners
Maintenance required:




Turn voltage off to unit (9,000 to 11,000
VDC supplied by cleaner’s transformer)
Remove the pre-filters and air cleaner
cells
Clean inside of cabinet
Clean pre-filters with a mild soap
solution
Electronic Air Cleaners
Maintenance required:




Wash air cleaner cells with a solution
of 3/4 cup of dishwasher detergent
and hot water
Vinegar can also be used to clean cells
Soak cells in solution for 15 to 20
minutes
Rinse until all the solution is removed
Electronic Air Cleaners
Maintenance required:


Inspect cells for any damage and
reinstall with pre-filters
Leave system’s blower on for 30
minutes with power off to air cleaner
to dry the cells thoroughly
Heat Recovery Ventilators
Maintenance required:


Filters should be changed monthly and
interior blower maintained on the same
schedule as the furnace
Drain pans and interior of unit:
– Clean interior surface and wipe the drain
pans with a soft cloth and a mild cleaning
solution
– Check condensate drain
Heat Recovery Ventilators
Maintenance required:

Heat Recovery Cores:
– Remove from unit
– Use warm water and a mild soap
– Soak recovery core in solution for about
three hours
– Allow to dry before reinstalling
Electrical Connections


Turn off voltage applied to the furnace
Make a visual inspection of all wire
terminals and wires
– Check for discoloration
– Check for frayed or damaged insulation
– Check for any loose connections and
retighten all accessible screw terminals if
needed
– Check fuse holders for tightness, if
applicable
Air Filters
Maintenance required:
 Can be either cleaned or replaced,
depending on type
 A clogged or dirty air filter will result in
the system going off on its high
temperature safety limit, resulting in
poor heating of the conditioned space
 Make sure to install air filters in the
correct direction of airflow
Air Filters


Some owners may choose to replace
their own filters or have their in-house
maintenance personnel install the filters
There are many different types of filters
available -- notify the customer of the
various types so the best filter can be
selected for the job
Fan Compartment

Check blower wheel for dirt build-up and
clean when required
– An important maintenance task
– Dirt on blower wheel will reduce CFM
delivered by fan
– This may be a time-consuming task
– May require removing entire drive
assembly
Fan Compartment
(Direct Driven Blowers)


Visually inspect fan motor for bearing
wear by spinning fan wheel and notice
how it slows down and stops
Check fan motor for excess end play
– Some motors may have up to 1/8” end play

Check motor bearing for “oval shape”
– There should be no vertical play with shaft

Lubricate motor, if required
Fan Compartment
(Belt Driven Blowers)

Check belt tension for proper
adjustment
– 3/8” to 1/2” depression with a 10 lb. force



If possible, use a belt tension gauge
Visually inspect belt, bearing and pulley
for signs of wear
Visually inspect pulley and drive
alignment
– use straight edge or string
Fan Compartment
(Belt Driven Blowers)


Check pulley and drive set screws for
tightness
Record belt size
– When possible leave an extra belt on the
job
– Mark belt size on unit

Lubricate motor and fan bearings, when
possible
– Some motors have sealed bearings and
external lubrication is not needed
Clean and Inspect
Condensate Drain System



Inspect condition of the condensate line
Clear lines with compressed gas, if
necessary
Inspect condensate pump, remove and
clean if required
Condensate Pumps
Maintenance required:





Remove pump from system
Remove reservoir from pump
Clean reservoir of any dirt or grime
and check float
Reinstall
Add water to system to check pumping
operation
Check Condition
of the Vent System




Inspect pipes for any cracks or weak
spots
Clean out chimney base if access door
is provided
If no access door is provided, remove a
section of pipe and examine for any
clogs or restrictions
Verify the vent system is pitched toward
the furnace 1/4” per foot
Draft Diverters
If the system has a draft diverter:



Check for obstructions
Check for signs of corrosion
Lightly tap area to see if walls
are rusted
Cleaning and
Inspection of Gas Burners





Remove and clean burners, mainly
multi-port burners only
Mono-port burners require little cleaning
Use a mild brush and shop vacuum
Do not damage or enlarge ports while
cleaning
Cleaning of burners may not be needed
on every inspection, but must be
checked
Cleaning and
Inspection of Gas Burners

Check burner alignment to ensure no
flame impingement is occurring on the
heat exchanger
– Flame impingement will cause CO


Make sure the burners are secure
Check crossover tubes to ensure proper
alignment
Heat Exchangers


Check for cracks
Can be inspected for cracks in one of
three ways:
– Visual Method
• Requires removing burners
• The use of a good mirror and strong
lamp
• Difficult to perform
– Air Flow Method
– Test Gas Method
Standing Pilot Systems



Remove and clean pilot assembly,
where required
Do not clean orifice with an object that
may change the size of the orifice
opening
Check and adjust pilot flame, if
necessary
Pilot Assemblies
Pilot flame should
impinge a height
of 3/8” to 1/2” on
the top of the
thermocouple
Thermocouples
Two dissimilar
metals are
welded together
at one end
When one of the junctions is heated and
the other end remains relatively cool,
a low electric DC voltage is produced
Thermocouples
The voltage generated depends on the
temperature difference between the hot
and cold junctions
Output Voltages



Normal output voltage of an
unloaded thermocouple is 26 to 32
milli-volts DC
The minimum acceptable output
voltage is 18 milli-volts DC
Drop out time of the pilot solenoid
should be within 2-1/2 minutes.
Direct Ignition
(Hot Surface Igniter)



Hot surface
igniter directly
lights burners
Made of
ceramic
Is very fragile
Uses flame rectification circuit
Direct Ignition
(Hot Surface Igniter)


During preventive maintenance
inspections, visually inspect for cracks
or breaks
At room temperature the resistance
should equal 45 to 90 ohms (if over
110 ohms, replace)
Thermostats

On mechanical thermostats check:
– That the thermostat is level
– That the heating anticipator setting is
properly set
– That the temperature gauge on the
thermostat is within 2°F of actual
temperature of the living space

Electronic thermostats only require
checking the accuracy of the temperature
gauge
Heating Anticipators




Wired in series with the controller
contacts
Set to match the amperage draw of
the heating controls
Too low of a setting will cause the
on cycle to be too short
Too high of a setting will cause the
on cycle to be too long
Sequence of Operation



A major part of a preventive
maintenance inspection is checking the
sequence of operation of a furnace
Necessary to verify the furnace is
operating safely and efficiently
Different furnace types will have
varying sequences of operation
Intermittent Pilot Furnaces
Sequence of operation:




Thermostat calls for heat
Spark is generated to light pilot
Once pilot flame is proven, the gas
valve opens and flame is produced
After a delay the indoor blower is
turned on
Standing Pilot Natural Draft
Sequence of operation:




Thermostat calls for heat
Gas valve opens
Burners are lit
After a delay, based on air
temperature the indoor
blower motor will come on
Standing Pilot Induced Draft
Sequence of operation:
 Thermostat calls for heat
 Induced draft blower comes on
 Once draft has been proven, the
gas valve opens and flame is
produced and the flame is
proved
 Indoor blower is turned on after a
delay
Direct Ignition
Condensing Furnace
Sequence of operation:
 Thermostat calls for heat
 Induced draft blower comes on
 Once the induced draft blower
builds a negative pressure in the
blower housing, the differential
pressure switch closes
 Hot surface igniter is energized
Direct Ignition
Condensing Furnace
Sequence of operation (cont.):



After a delay the gas valve opens
and flame is produced
Once the flame is proved, the gas
valve will remain energized
Indoor blower is turned on after a
delay
Check & Record
Manifold Gas Pressure



Compare with manufacturer’s
specifications
Normally natural gas is 3.5” w.c. at the
outlet of the gas valve
Normally LP is 11” at the outlet of the
gas valve
Flame Color



The flame should be a well-defined
blue with slightly orange tips
If yellow tips are observed, it is a sign
of incomplete combustion and the
cause should be found and rectified
A yellow-tipped flame is producing CO
which is not a desired result of
combustion
Flame Conditions
Problem
Cause
Remedy
Lifting Flame
Too much primary
air
Gas pressure too
high
Incorrect orifice
Decrease primary
air
Reduce gas
pressure
Check and replace
if needed
Yellow
Tipping
Shortage of
primary air
Increase primary
air
Shortage of total
combustion air
Clean burner
Incorrect orifice
Check and replace
if needed
Flame Conditions
Problem
Flashback
Extinction
Pop
Wavering
Flames
Cause
Remedy
Primary airflow too Decrease
high
primary air
Gas flow is too low Check gas
input
Replace burner
Defective gas
Replace gas
valve
valve
Drafts in
combustion
chamber
Cracked heat
exchanger
Check furnace
panels
Replace
Flame Conditions
Problem
Delayed
Ignition
Cause
Remedy
Improper gas
pressure
Slow opening gas
valve
Misdirected pilot
flame
Adjust gas
pressure
Replace gas
valve
Redirect
Dirty orifice or
burners
Clean
Drafts across the
burners
Check furnace
panels
Flame Rollout Shortage of
combustion air
Check for
blockage
Combustion Testing
Combustion Efficiency


Measuring the CO2 and flue gas
temperature is a means of determining
the combustion efficiency
Steady state efficiency is the point at
which combustion gas content reaches
equilibrium and the stack temperatures
stabilize
Combustion Tests





Measure ambient temperature and
the stack temperature to obtain
the net stack temperature
Measure draft pressure
Measure the carbon dioxide(CO2) level
Measure the oxygen (O2)level
Measure the carbon monoxide (CO)
level
Category I Appliance
Fan Assisted Furnaces
Category I
Appliance Test Points
Category IV Appliances
Checking Airflow




Tested by measuring the temperature
rise across the heat exchanger
Generally low-efficiency furnaces will
have a temperature rise of 75°F to
100°F
Generally high-efficiency furnaces will
have a temperature rise of 40°F to 70°F
Always look on the data plate of the
furnace for the correct range
Temperature Rise


Always check the supply air
temperature out of the line of sight of
the heat exchanger, and the return air
temperature as close as possible to the
heat exchanger
Before checking the temperature rise of
a furnace, make sure the filter is clean
and the airflow is not being restricted
Temperature Rise




All registers and dampers must be
open
The system should be operating for at
least 15 minutes
Use the same type thermometer for
measuring the supply and return
temperatures
Before checking the temperature rise,
compare the accuracy of thermometers
Temperature Rise


A temperature rise that is higher than
the range stated on the furnace
indicates a shortage of airflow across
the heat exchanger
A temperature rise that is lower than
the range stated on the furnace
indicates too much airflow across the
heat exchanger
Adjusting the Fan Speed
A direct drive blower’s fan speeds can
usually be changed by selecting the
appropriate speed tap
Common Color Coding:
• White = common
• Black = high speed
• Yellow = medium high speed
• Blue = medium low speed
• Red = low speed
Adjusting the Fan Speed

Belt-driven blowers can usually be
adjusted by changing the flange on the
motor pulley
– Adjusting the pulley flange towards the fixed
flange will increase the speed of the blower

Sometimes the pulley will need to be
changed, using the formula:
Diameter(drive) = Diameter(driven) X (rpm(fan)/rpm(motor))
On belt driven fans
always check the
amperage draw of the
motor after making any
adjust to the fan speed
Safety Controls Checks



Verify the operation of the high
temperature switch
Block return airflow completely and
observe the gas valve shutting down
On induced draft furnaces, remove one
end of the rubber hose from the air
pressure switch and observe the gas
valve shutting down
THE END