WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY
HVAC Distribution
Systems
1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Learning Objectives
HVAC DISTRIBUTION SYSTEMS
By attending this session, participants will be able to:
• Name functions of the components of forced warm air,
hot water, and steam distribution systems.
• Demonstrate common diagnostic and assessment
methods for ducted distribution systems.
• Describe common problems for each distribution
system type.
• Explain solutions to these common problems.
2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Good Ducted System Design
HVAC DISTRIBUTION SYSTEMS
A well-designed duct system:
• Provides conditioned air to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned rooms.
• Is properly sized so that static pressure is within
manufacturer specifications.
• Is sealed to provide proper airflow and prevent air from
entering the house or duct system from polluted zones.
• Has balanced supply and return airflows to maintain a
neutral pressure in the house.
• Minimizes duct air temperature losses between the air
handler and supply registers.
3 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Forced Air Distribution System
HVAC DISTRIBUTION SYSTEMS
The parts include:
• An air handler at the furnace.
• A heat exchanger where the heat from combustion is
transferred to the distribution air.
• A supply air plenum to which the supply trunks are attached.
• Branches attached to the supply trunk.
• Supply registers through which conditioned air flows to the
living space.
• Return grilles through which air flows back to the furnace.
• Return branches and trunks attached to the return plenum.
4 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Ducted Distribution System
HVAC DISTRIBUTION SYSTEMS
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Ducted Distribution System, Cont’d
HVAC DISTRIBUTION SYSTEMS
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Open Returns
HVAC DISTRIBUTION SYSTEMS
Open return
Draft hood
(open at bottom)
Photo Courtesy of PA Weatherization Training Center
7 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Distribution System Components
HVAC DISTRIBUTION SYSTEMS
Atmospheric
Gas Furnace
Find the:
1. Circulating fan
2. Air filter
3. Cold air return
4. Heat exchanger
5. Warm air to house
Source: Heating with Gas, Natural Resources Canada, 1998.
8 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Function of Heat Exchanger
HVAC DISTRIBUTION SYSTEMS
• The furnace heat exchanger is where the heat from
combustion gases—usually between 70% and
95%— is transferred to the distribution air in the
ductwork.
• The heat exchanger is an extremely important part
of any furnace because it can have a significant
impact on efficiency and health and safety.
• Combustion byproducts must not mix with
distribution air.
9 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Heat Exchanger Leakage Testing
HVAC DISTRIBUTION SYSTEMS
Test methods:
1. Visual inspection
Damaged area of
heat exchanger
2. Inspection with small torch
3. CO reading
4. Wavering flame
5. Tracer gas
Photo courtesy of New River Center for
Energy Research and Training (NRCERT)
10 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Ductwork Efficiency
HVAC DISTRIBUTION SYSTEMS
• Specify duct sealing where ducts
are located in unconditioned
spaces.
• Ducts in unconditioned spaces
should be insulated to
recommended levels.
• Seal all returns in spaces where
atmospheric fossil fuel appliances
are located.
It is often necessary to remove duct
insulation to properly seal ducts.
Seal with mastic, then re-insulate.
Photos courtesy of NRCERT
11 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Ductwork
HVAC DISTRIBUTION SYSTEMS
Photos courtesy of R. Karg
This sheet metal ductwork
is located within the
building envelope, so it
does not need to be
insulated.
12 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Ducted System Controls
HVAC DISTRIBUTION SYSTEMS
The primary controls are:
• Thermostat.
• Fan and limit control.
• Balancing dampers.
• Motorized dampers (these are not common).
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Furnace Thermostat
HVAC DISTRIBUTION SYSTEMS
The thermostat
activates the burner
on a furnace.
The fan and limit
switch turns the air
handler blower on
and off.
Photo courtesy of R. Karg
14 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Fan and Limit Control
HVAC DISTRIBUTION SYSTEMS
This control turns the
air handler blower on and
off at set temperatures.
This is the fan control.
It also shuts down the
blower if the heat exchanger
area gets too hot (usually at
about 200). This is
the limit control.
Recent versions are
electronic and cannot be
adjusted in the field.
Graphic source: Heating with Gas, Natural Resources Canada, 1998.
Photo courtesy of Honeywell.
15 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Balancing Dampers
HVAC DISTRIBUTION SYSTEMS
Dampers help control airflow to rooms.
Balancing damper
Graphic source: Heating with Gas, Natural
Resources Canada, 1998.
Manual balancing dampers are not as common
as they should be. Sometimes they need to be added.
16 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Motorized Dampers
HVAC DISTRIBUTION SYSTEMS
Motorized dampers are
uncommon.
Motorized dampers are
used for zoning a
ducted distribution
system, rather than for
balancing.
When a zone requires
heat, the thermostat of
that zone opens the
zone damper and
activates the furnace
burner.
Photo courtesy of R. Karg
17 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Common Ductwork Problems
HVAC DISTRIBUTION SYSTEMS
Common problems include:
• Duct leakage to/from the outdoors.
• Restricted return side.
• System not balanced.
• Temperature too high or too low at heat exchanger.
• Static pressure out of range.
• Airflow of air handler fan not matched to system.
• People live within the distribution system. Closing a
bedroom door or covering a register or grille can
significantly alter airflow.
18 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Diagnostics for Ductwork
HVAC DISTRIBUTION SYSTEMS
Diagnostics include:
• Pressure pan (duct leakage).
• Duct blower (duct leakage).
• Static pressure.
• Temperature rise.
• Room-to-room pressure differences (door restrictions).
• Air handler blower CFM flow.
19 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Pressure Pan
HVAC DISTRIBUTION SYSTEMS
Test the duct system with
a pressure pan and blower
door to identify:
Pressure
pan testing
of the duct
system
• Leakage to the outdoors
when ducts are located
outside the thermal
boundary.
• Leakage pathways from
duct-containing building
cavities to the outdoors (e.g.,
floor-joist cavities adjacent to
porch roofs, cantilevers).
Photo courtesy of NRCERT
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Pressure Pan Procedure Summary
HVAC DISTRIBUTION SYSTEMS
• Depressurize house to
50 Pa with blower door.
• Test each register and
grille. Document
readings.
Photo courtesy of NRCERT
The handle allows for
easy testing of
hard-to-reach ducts.
• Registers too large or
oddly shaped may be
covered with plastic and
taped on edges.
• Seal duct leaks and
retest.
• Goal = readings lower
than 1 Pa
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Pressure Pan Use
HVAC DISTRIBUTION SYSTEMS
Sample mobile home duct pattern
Bedroom
Bedroom
Bath
Furnace Closet (living room)
Living Room
Kitchen
Kitchen
0.8 Pa
1.2 Pa
2.4 Pa
2.6 Pa
2.6 Pa
1.2 Pa
0.5 Pa
Total:
10.7 Pa
2.4 Pa at the bath register and 2.6 Pa
at the living room register indicate a
large leak between them, probably
at the furnace plenum.
Photo courtesy of NRCERT
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Duct Blower for Duct Leakage
HVAC DISTRIBUTION SYSTEMS
Manometer
Use duct
pressurization
testing to quantify:
• Total duct leakage
(to indoors and
outdoors).
• Duct leakage
to outdoors.
Duct blaster
Photo courtesy of The Energy Conservatory
23 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Duct Blower Procedure
Summary #1
HVAC DISTRIBUTION SYSTEMS
To test for total duct leakage:
1. Open a window or door to the outdoors.
2. Install duct blower to the air handler compartment.
3. Temporarily seal all supply registers and return grilles.
4. Insert manometer hose into a supply duct.
5. Open up rooms containing ducts.
6. Pressurize the ducts to 25 Pa and record the airflow.
24 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Duct Blower Procedure
Summary #2
HVAC DISTRIBUTION SYSTEMS
To test for duct leakage to outdoors:
1. Close all exterior windows and doors.
2. Set up blower door to pressurize the house.
3. Connect duct blower to air handler compartment and
manometer hose to air handler compartment.
4. Temporarily seal all supply registers and return grilles.
5. Pressurize the ducts to 25 Pa.
6. Pressurize the house until the pressure difference of
the house and the ductwork is 0 Pa.
7. Record the airflow at the duct blower.
25 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Room-to-Room Imbalances #1
HVAC DISTRIBUTION SYSTEMS
Closed doors that prevent
supply air from getting back
to a return cause positive
pressures in those rooms
with supply vents. . .
…which starves the return
for air, causing negative
pressure in the zone where
the return is located.
Return
Supply
Closed door
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Room-to-Room Imbalances #2
HVAC DISTRIBUTION SYSTEMS
Master
Bedroom
Utility Room
Kitchen
Whole-house return in hallway
Living Room
Bedroom
Bath
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Room-to-Room Imbalances #3
HVAC DISTRIBUTION SYSTEMS
Measure room-to-room pressure imbalances
Room pressure imbalances over 3 Pa should be
remedied by adding supply or return air. Then retest.
Photo courtesy of
PA Weatherization Training Center
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Room-to-Room Imbalances #4
HVAC DISTRIBUTION SYSTEMS
Solutions
1. Undercut door.
2. Add jumper duct.
3. Add door grille.
4. Add wall grille.
5. Add transfer grille.
6. Install return in
affected room.
Graphic source: Air Distribution System Design, DOE, 2003.
Find the size of the free vent area of your solution by opening the door while the
air handler is running. When the manometer reading falls below 3 Pa, measure
the in2 of door opening. This is the in2 of free opening for your solution.
29 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Measuring Static Pressure #1
HVAC DISTRIBUTION SYSTEMS
Magnet
Photo courtesy of Rob deKieffer
Point the tip into the air stream
30 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of R. Karg
Static pressure tip
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Measuring Static Pressure #2
HVAC DISTRIBUTION SYSTEMS
Measuring External Static Pressure
• Check nameplate for External Static Pressure (ESP).
• Measure both return and supply sides of the air handler
as the unit was shipped.
o Measure at inlet and outlet of blower.
o Have a clean filter in place (suggested).
o Don’t measure beyond the A/C coil unless it shipped
with unit.
• Add return and supply pressures together, IGNORING the
negative sign.
31 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Measuring Static Pressure #3
HVAC DISTRIBUTION SYSTEMS
General External Static Pressure and Fan Relationship
External Static Pressure
Air Handler Fan Flow
IWC (Pa)
Cubic Feet per Minute
0.69 (173)
1,350
0.62 (155)
1,400
0.55 (138)
1,450
0.47 (118)
1,500
0.39 (98)
1,550
0.31 (78)
1,600
If the static pressure is too high, the fan flow will drop.
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Measuring Static Pressure #4
HVAC DISTRIBUTION SYSTEMS
Measuring External Static Pressure
• If ESP is too high, the airflow might be blocked or the ductwork might
be too small or restricted.
• If ESP is too low, the ductwork might be very leaky or the fan might be
dirty or damaged.
• Typical ESP totals are around 0.5 IWC or 125 Pa with an air
conditioning coil and filter.
• Typical ESP totals are around 0.25 IWC or 62 Pa without an air
conditioning coil and filter.
• It is preferred to have the return and supply sides of similar
magnitudes, for example, a return of -34 Pa and supply of +31 Pa.
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Temperature Rise Test #1
HVAC DISTRIBUTION SYSTEMS
• Place thermometer in supply side as close to furnace as possible but
out of “sight” of the heat exchanger.
o Use manufacturer’s recommended measurement method, or
o Use the four-corner method (measure at each corner or supply
plenum and average readings).
• Place thermometer in return side.
• Fire furnace.
• When the supply-side temperature reaches steady state, subtract
return-side from supply-side temperature to get temperature rise.
• Check specified temperature rise on furnace name plate. Actual
should be in the middle of the nameplate range.
34 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Temperature Rise Test #2
HVAC DISTRIBUTION SYSTEMS
Measuring Temperature Rise &
Calculating CFM
The temperature
rise for this example
is 70:
145 supply side
-75 return side
70 temperature rise
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Temperature Rise Test #3
HVAC DISTRIBUTION SYSTEMS
Excessive temperature rise can result from:
• Low fan output.
o Wrong fan speed, bad motor bearings, low voltage to
motor, dirty blower wheel, wrong motor rotation,
slipping blower belt.
• Low airflow from restrictions in system.
o Undersized or restricted ducts, dirty filter, dirty cooling
coil.
• Overfired burner (gas pressure or oil nozzle).
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Temperature Rise Test #4
HVAC DISTRIBUTION SYSTEMS
Low temperature rise can result from:
• Excessive fan speed.
• Excessive duct leakage.
• Underfired burner.
o Low gas pressure.
o Oil nozzle not matched with airflow rate.
37 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Temperature Rise Test #5
HVAC DISTRIBUTION SYSTEMS
Temperature rise that is too high can:
• Damage the heat exchanger.
• Cause rocking on the high limit.
Temperature rise that is too low can:
• Lead to condensation.
• Cause excessive soot buildup.
• Lead to occupant discomfort.
38 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Measuring Air Flow at Air Handler #1
HVAC DISTRIBUTION SYSTEMS
TrueFlow ® Air Handler Flow Meter
Measures airflow
in residential
air handlers
#20
#14
Photos courtesy of The Energy Conservatory
39 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Measuring Air Flow at Air Handler #2
HVAC DISTRIBUTION SYSTEMS
General Minimum Airflow Values
Airflow in CFM
Furnace BTUH Input
500
Less than 60,000
700
60,000 to 79,999
900
80,000 to 99,999
1,200
More than 100,000
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Assessing Ductwork #1
HVAC DISTRIBUTION SYSTEMS
Analysis
Existing about
Ductwork
-1
Interviewof
occupants
the thermal
comfort of the
existing system.
Ask about:
• Uncomfortable rooms.
• Excessive noise.
• Frequent cycling
of furnace.
Plumbing through return duct!
Photo courtesy of R. Karg
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Assessing Ductwork #2
HVAC DISTRIBUTION SYSTEMS
Analysis of Existing Ductwork - 2
Inspect air handler and ductwork for such things as:
• Disconnected ducts.
• Duct leakage.
Disconnected duct!
• Restricted returns.
• Panned floor joists.
• Ducts in unconditioned
spaces.
• Balancing dampers.
Photo courtesy of R. Karg
42 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of R. Karg
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Assessing Ductwork #3
HVAC DISTRIBUTION SYSTEMS
Do technical testing and appraisal of the duct system
and equipment.
• Duct leakage
o Pressure pan testing
o Duct blower testing
• Room-to-room pressure
imbalances
• Static pressure
Very dirty blower vanes!
• Temperature rise
• Blower CFM
43 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photo courtesy of NRCERT
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Assessing Ductwork #4
HVAC DISTRIBUTION SYSTEMS
Analysis of Existing Ductwork - 5
Determine strategies for duct repair:
• Write down possible problems.
• Determine required alterations to furnace and ductwork.
• Decide on consumer education strategies.
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Good Hot Water Distribution
Design
HVAC DISTRIBUTION SYSTEMS
Good design:
• Provides conditioning to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned
rooms.
• Heats the dwelling quietly.
Hot water or steam distribution is often referred to as
“hydronic.”
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Hot Water Distribution System
HVAC DISTRIBUTION SYSTEMS
The parts include:
• Thermostat(s) that activate the circulator pump.
• Circulator pump(s). Might include zone valves rather than
two or more circulator pumps.
• Aquastat control.
• A heat exchanger where the heat from combustion is
transferred to the distribution water.
• Supply and return piping at boiler.
• The expansion tank.
• Hot water baseboard units (convector) where the thermal
energy is transferred to the conditioned rooms.
46 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Series Loop Hot Water System
HVAC DISTRIBUTION SYSTEMS
A series loop hot
water distribution
system is probably
the most common
system layout
because it is the
least expensive.
Based on graphic from the International Association of Certified Home Inspectors, Inc.
47 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Series Loop Hot Water Baseboard
HVAC DISTRIBUTION SYSTEMS
Typical hot water baseboard distribution
Damper fin
Photos courtesy of Slant/Fin
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Expansion Tanks
HVAC DISTRIBUTION SYSTEMS
Old-style tanks (above) and
newer tanks (right) allow for
expansion of heated water and
contraction of cool distribution
water.
49 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
Photos courtesy of R. Karg
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Hot Water Distribution Controls
HVAC DISTRIBUTION SYSTEMS
Basic controls include:
Thermostat
Circulator pump(s)
Zone valves
Aquastat
50 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Boiler Thermostat
HVAC DISTRIBUTION SYSTEMS
The thermostat activates
the boiler circulator or
zone valve and circulator.
The aquastat controls
the burner.
Photo courtesy of R. Karg
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Boiler Aquastat
HVAC DISTRIBUTION SYSTEMS
An aquastat:
1. Maintains boiler water
temperature.
2. Provides high-limit
temperature protection.
3. Will not allow circulator
to operate if boiler
water temperature is
too low.
Photo courtesy of R. Karg
Normally, the aquastat control is covered.
Also assists with DHW
temperature control if the
water heater is tankless or
indirect-fired.
52 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Zone Valves
HVAC DISTRIBUTION SYSTEMS
Zone valves are
controlled by
thermostats in each
zone.
This house has 3
zones with one
thermostat for each.
Photo courtesy of R. Karg
Zone valves take the place of circulators.
The 4th zone valve
is for domestic hot
water from the
boiler.
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Potential Problems with
Hot Water #1
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of R. Karg
Poor maintenance:
• If a hot water distribution
system is maintained
properly, there is little that
can go wrong.
o Oil-fired boilers should be
cleaned and tuned every
year.
o Gas-fired boilers should be
cleaned and tuned once
every three years.
54 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Potential Problems with
Hot Water #2
HVAC DISTRIBUTION SYSTEMS
Poor expansion tank maintenance
Older tanks (above) should
be drained and refilled annually.
Newer expansion tanks (right)
require very little maintenance.
Photos courtesy of R. Karg
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Potential Problems with
Hot Water #3
HVAC DISTRIBUTION SYSTEMS
Air bleeder vent
Air in the distribution system
If the air bleeder valve malfunctions, air will
not be purged from the distribution system.
This air (oxygen) will create sludge and make
the system noisy as the air is pumped with
the water.
Expansion tank
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Good Steam Distribution Design
HVAC DISTRIBUTION SYSTEMS
A good design:
• Provides conditioning to meet all room heating loads.
• Provides thermal comfort evenly in all conditioned
rooms.
57 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Steam Distribution System
HVAC DISTRIBUTION SYSTEMS
The parts include:
• A thermostat(s) that activates the circulator pump.
• Pressure control (Pressuretrol).
• A heat exchanger where the heat from combustion is
transferred to the distribution water/vapor.
• Supply and return piping at boiler.
o For one-pipe distribution, the supply and return pipes
are the same.
o For two-pipe distribution, there are separate supply
and return pipes.
• Steam radiators that transfer thermal energy to the
conditioned rooms.
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Steam Distribution Controls and
Gauges
HVAC DISTRIBUTION SYSTEMS
Basic controls include:
• Thermostat
• Pressure control (Pressuretrol)
• Sight or gauge glass
• Low-water cutoff
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Steam Boiler Thermostat
HVAC DISTRIBUTION SYSTEMS
The thermostat activates
the steam boiler burner.
The Pressuretrol turns the
burner off when the set
pressure is reached.
Photo courtesy of R. Karg
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Steam Boiler
HVAC DISTRIBUTION SYSTEMS
Pressuretrol
(pressure control)
Sight glass
Low-water cutoff
Oil burner
Photo courtesy of R. Karg
61 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012
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Steam Distribution Controls
HVAC DISTRIBUTION SYSTEMS
Photo courtesy of R. Karg
Sight (gauge) glass
The low-water cutoff will
shut off the burner if the
water falls to an unsafe
level. This is required by
code.
The sight or gauge glass
provides an easy way to
determine the water level
in a steam boiler.
Low-water cutoff
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Pressure Control for Steam
HVAC DISTRIBUTION SYSTEMS
This device determines
the operating range of
the boiler during the
heating cycle.
Photo courtesy of Honeywell Controls
When the thermostat
calls for heat, the burner
will cycle up to the cutout pressure setting of
the Pressuretrol. The
burner will then shut off.
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One-Pipe Steam Distribution
HVAC DISTRIBUTION SYSTEMS
One-Pipe Steam Distribution
Both steam and
condensate use the
same pipe.
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT
Industries, 1999, p. 2, www.hoffmanspecialty.com.
Steam travels to
each radiator,
condenses (giving
off heat), and flows
back to the boiler
through the same
pipe as condensed
water.
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Two-Pipe Steam Distribution
HVAC DISTRIBUTION SYSTEMS
Steam moves to the
radiators in one pipe
and the condensate
flows back to the
boiler through the
other pipe.
These pipes are
usually a smaller
diameter than
one-pipe systems.
Graphic based on Basic Steam Heating Systems, Hoffman Specialty, ITT
Industries, 1999, p. 2, www.hoffmanspecialty.com.
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Potential Problems with Steam #1
HVAC DISTRIBUTION SYSTEMS
Steam distribution pipes
are sometimes covered
with asbestos insulation.
If this material is friable,
be careful; it might be
best to avoid blower door
testing.
Photo courtesy of R. Karg
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Potential Problems with Steam #2
HVAC DISTRIBUTION SYSTEMS
If one- or two-pipe
radiators don’t heat up,
the supply valve may be
closed or the air
valve may be blocked.
Supply valve
Air valve
Two-pipe radiator
Photo source: The Open Fire Centre Ltd., Yorkshire St.,
Oldham, Lancashire, UK. www.fireplaces-oldham.co.uk.
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Potential Problems with Steam #3
HVAC DISTRIBUTION SYSTEMS
Steam pressure is
often set too high.
This can cause
distribution problems
and wastes energy.
For most residential
low-pressure, onepipe systems, 2 psi
cut-out pressure or
less will work fine and
maximize efficiency.
Photo courtesy of Bill Van der Meer
High pressure can cause distribution problems and
waste energy.
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Potential Problems with Steam #4
HVAC DISTRIBUTION SYSTEMS
When replacing a steam
boiler, the new unit must
be sized to match the
installed radiation, rather
than the heat load of
the house.
Photo courtesy of R. Karg
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Summary #1
HVAC DISTRIBUTION SYSTEMS
• The function of all distribution systems is to provide even
thermal comfort in all rooms of the home.
• Major components of forced air distribution systems include an
air handler, heat exchanger, supply air plenum, supply and
return registers, grilles, branches, and ducts.
• Forced air system diagnostic procedures include duct leakage
testing, measuring static pressure, temperature rise, room-toroom pressure imbalances, and airflow across the heat
exchanger.
• Common problems associated with ducted systems include
room pressure imbalances, improper temperature rise, and
energy wasted through duct leakage to the outdoors.
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Summary #2
HVAC DISTRIBUTION SYSTEMS
• Major components of hot water distribution systems include the
thermostat, circulator pump, aquastat control, heat exchanger, supply
and return piping, expansion tank, and hot water baseboard units.
• Major components of steam distribution systems include the
thermostat, pressure control (Pressuretrol), heat exchanger, supply and
return piping at the boiler, steam radiators, sight glass or gauge glass,
and low-water cutoff.
• Some common problems associated with hot water or steam
distribution include expansion tank degradation, low water levels
(steam), or improper sizing once the home is weatherized.
• Compared with ductwork, hot water and steam distribution are relatively
trouble-free, and diagnostic procedures are easy. We merely ask the
occupants if there are problems with the thermal comfort of the home
and conduct a simple inspection of the distribution components.
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