Overview Heating and Cooling Systems A person’s comfort in an environment depends on the temperature, relative humidity, mean radiant temperature, and air movement.  A weatherization service provider should be aware of these four factors. There are many types of heating and cooling systems that may be present in homes that need to be weatherized.  A weatherization service provider should be able to differentiate between the types of systems and recognize problems with a system. Lastly, a weatherization service provider should be able to detect leaks in duct systems using various testing methods.  After the leaks have been discovered, the provider should be able to seal the leaks to improve the efficiency of the system. Learning Objectives Upon completion of this module, you should be able to: 6A analyze the myriad of factors that influence human comfort. 6B recall the differences between various state-of-the-art home heating and cooling systems. 6C list the various tests that can be used to detect home heating/cooling system leaks. 6D explain the various methods used to seal duct leaks in homes. Module 5 Reading Assignment Krigger, J., & Dorsi, C. (2012).  Residential Energy: Cost Savings and Comfort for Existing Buildings (6th ed.).  Helena: Saturn Resource Management, Inc.  Chapters 3 (pp. 86-100), 6, and 8. Supplemental Reading Assignments (Required): EERE (2011).  HVAC: a guide for contractors to share with homeowners (Report No. PNNL-20241).  Washington, D.C.: Buildings technologies program (pp. 1-68). EPA (2009).  A guide to energy efficient heating and cooling[Brochure].  Washington, D.C., (pp. 1-24). EPA (2009).  Duct sealing [Brochure]. Washington, D.C., (pp. 1-5). Friedman, G. (2004).  “Too hot/too cold diagnosing occupant complaints.”  ASHRAE, (pp. 157-163). Lecture Notes Heating and Cooling Systems There are four factors that contribute to a person’s comfort in a particular environment: air temperature, relative humidity, the mean radiant temperature, and the presence of air movement.  When the temperature, moisture, radiant temperatures, and moving air are controlled in any environment, people will be comfortable. Relative Humidity The amount of moisture in the air is one of the factors that directly affects comfort whether a person is inside or outside.  Relative Humidity (RH) is the amount of moisture in the air compared to the total amount of water that could be in the air if it were totally saturated.  A weatherization service provider can measure relative humidity using a hygrometer or a relative humidity and temperature meter.  A psychrometer is a basic hygrometer that is made of two thermometers.  A reading of 50 percent relative humidity means that the air, at a specific temperature, contains 50 percent of the total amount of water it is capable of maintaining for saturation. Mean Radiant Temperature The mean radiant temperature is the average temperature of the surfaces in the environment.  Warm air can hold more moi.

1. Overview
Heating and Cooling Systems
A person’s comfort in an environment depends on the
temperature, relative humidity, mean radiant temperature, and
air movement. A weatherization service provider should be
aware of these four factors.
There are many types of heating and cooling systems that may
be present in homes that need to be weatherized. A
weatherization service provider should be able to differentiate
between the types of systems and recognize problems with a
system.
Lastly, a weatherization service provider should be able to
detect leaks in duct systems using various testing methods.
After the leaks have been discovered, the provider should be
able to seal the leaks to improve the efficiency of the system.
Learning Objectives
Upon completion of this module, you should be able to:
6A
analyze the myriad of factors that influence human comfort.
6B
recall the differences between various state-of-the-art home
heating and cooling systems.
6C
list the various tests that can be used to detect home
heating/cooling system leaks.
6D
explain the various methods used to seal duct leaks in homes.
Module 5 Reading Assignment
Krigger, J., & Dorsi, C. (2012). Residential Energy: Cost
Savings and Comfort for Existing Buildings (6th ed.). Helena:

2. Saturn Resource Management, Inc. Chapters 3 (pp. 86-100), 6,
and 8.
Supplemental Reading Assignments (Required):
EERE (2011). HVAC: a guide for contractors to share with
homeowners (Report No. PNNL-20241). Washington, D.C.:
Buildings technologies program (pp. 1-68).
EPA (2009). A guide to energy efficient heating and
cooling[Brochure]. Washington, D.C., (pp. 1-24).
EPA (2009). Duct sealing [Brochure]. Washington, D.C., (pp.
1-5).
Friedman, G. (2004). “Too hot/too cold diagnosing occupant
complaints.” ASHRAE, (pp. 157-163).
Lecture Notes
Heating and Cooling Systems
There are four factors that contribute to a person’s comfort in a
particular environment: air temperature, relative humidity, the
mean radiant temperature, and the presence of air movement.
When the temperature, moisture, radiant temperatures, and
moving air are controlled in any environment, people will be
comfortable.
Relative Humidity
The amount of moisture in the air is one of the factors that
directly affects comfort whether a person is inside or outside.
Relative Humidity (RH) is the amount of moisture in the air
compared to the total amount of water that could be in the air if
it were totally saturated. A weatherization service provider can
measure relative humidity using a hygrometer or a relative
humidity and temperature meter. A psychrometer is a basic
hygrometer that is made of two thermometers. A reading of 50
percent relative humidity means that the air, at a specific
temperature, contains 50 percent of the total amount of water it
is capable of maintaining for saturation.
Mean Radiant Temperature
The mean radiant temperature is the average temperature of the
surfaces in the environment. Warm air can hold more moisture
than cold air. If the amount of moisture in the air remains the

3. same (measured in grains of water vapor per pound of dry air),
the relative humidity will change according to the temperature
of the air. At an air temperature of 60ºF with 40 grains of
moisture, the relative humidity is approximately 55 percent. If
the temperature changes to 90ºF and the moisture remains the
same, the relative humidity changes to approximately 18
percent. The normal comfort range for relative humidity in
homes is between 30 percent and 50 percent.
Dew Point and Condensation
The dew point is the temperature of the air in an environment at
which water vapor in the air will change phase to liquid. This
change in phase from vapor to liquid is referred to as
condensation. Condensation occurs when the temperature of a
surface is less than the dew point. It is a major ongoing
building issue in homes because of the degradation of window
and wall components.
Example: Typical aluminum windows are highly conductive and
reflect exterior temperatures on the inside surface. An
aluminum window with a single pane of glass will have a U-
factor of approximately 1.0. With an exterior temperature of
20ºF reflected on the window components, condensation can
occur when the interior RH is as low as 25 percent.
Sometimes condensation occurs within a wall cavity. In cold
climates, if warm, moist air is forced into wall cavities, because
the building is under positive pressure during cold weather, and
it comes into contact with surfaces below the dew point,
condensation will occur and major damage can be done to the
wall components in a very short period of time.
Visual manifestations of condensation include ceiling supply
registers when the unit is off and there is an unvented heater in
the house, fungal growth on cold walls behind furniture or on a
ceiling where there is sparse or no insulation, sagging tiles in
the ceiling over a basement, stains on attic insulation from air
leaving the conditioned space during the heating season, and
rusty nails on the floor above a vented crawl space.
Movement of Heat and Conditioned Air

4. The movement of heat throughout a building is accomplished
through conduction, convection, or radiation. Conduction is the
process in which heat is transferred through solid matter from
particle to particle. Conduction is slowed by insulation.
Insulating ceilings, walls, attics, and floors decreases the
amount of heating or cooling needed by providing resistance to
the flow of heated air.
Convection is the process in which heat is transferred by the
actual movement of the warmed matter. Convection is the
transfer of heat energy in a gas or liquid by movement of
currents. Convection is interrupted by physical barriers.
Radiation is the process in which electromagnetic waves
directly transport energy through space. Sunlight is a form of
radiation that travels through space to Earth without the
assistance of fluids or solids. Heat energy transferred by
radiation can be interrupted and reflected by materials.
The building envelope, which is discussed in detail in Module
4, is designed to control conditioned air. Conditioned air has
been warmed, cooled, or has had moisture added to or removed
from it. Conditioned air moves through buildings and affects
comfort, health, and energy costs. The movement of
conditioned air through the building envelope affects the quality
of indoor air.
Keeping the attic ventilated is an important part of restricting
the flow of hot and cold air into the interior of a building. If an
attic is not properly insulated and vented, hot air will filter into
the building during the summer and increase the cost of
cooling. If the attic is not kept cool in colder climates, snow on
the roof can melt and refreeze, which damages the roofing
material.
Different types of attic ventilation systems include gable, ridge,
roof, and soffit vents.
Heating Degree Day
A Heating Degree Day (HDD) is the measurement used to
determine the heating requirements for structures in differing
climate zones. The HDD is the number of degrees per day that

5. the daily average temperature is below a base temperature of
65ºF. The daily average temperature is the mean of the
maximum and minimum recorded temperatures.
Example: On a day when the high temperature is 40ºF and the
low temperature is 10ºF, the mean daily temperature is 25ºF
[(40 + 10) ÷ 2]. This mean temperature is subtracted from 65ºF
to find the HDD, which is 40 HDDs (65-25 = 40).
Example: Anchorage, Alaska has approximately 10,864 HDDs
whereas Honolulu, Hawaii has 0 HDDs.
A weatherization service provider can calculate the HDD to
help determine what the building’s heating requirements are, if
the current system is sufficient, or if changes should be made.
Heating Equipment
There are numerous types of heating systems used in the United
States and most homes have some type of heating device. Types
of heating systems include:natural gas.
fuel oil and propane furnaces.
electric appliances.
boilers with radiant flooring.
hot water and steam heating systems.
new integrated heating systems.
wood stoves.
Combustion Appliances
Combustion appliances are the most widely used type of heating
system. Most houses have a forced air distribution system,
which has a fan that forces air through a delivery system to the
structure. The heating portion of the system is the furnace or
air handler. A furnace is a combustion appliance in which heat
is captured from the burning of a fuel for the purpose of heating
air for distribution to a house.
A furnace has several basic components: a combustion chamber,
fan, an atmospheric (or closed gas) burner, a heat exchanger,
and a flue. A heat exchanger is a device used to transfer heat
from a fluid (liquid or gas) to another fluid when the two fluids
are physically separated. A flue is a structure in which
combustion gases collect until they are emitted into the

6. atmosphere.
The nameplate of a furnace provides basic information about the
unit, which may include input and output BTUH, the
temperature rise range, type of fuel, manufacturer name and
date, and the model and serial numbers.
Older Furnace Models
Older furnaces were atmospheric draft heaters, which meant that
the venting of the flue gases to the outside of the home was
dependent on the principle of draft. The principle of draft
states that hot air rises. Some modern improvements to this
type of system involve fan-assisted draft, which uses a fan to
force the flue gases to go outside.
Furnaces with efficiency ratings of 80 percent or less take their
combustion air from the area in which the furnace is installed
and are referred to as open combustion units. These older
furnaces have a fan for drawing a metered amount of
combustion gases through the heat exchanger and include a
draft diverter to moderate excessive updrafts and downdrafts.
Newer Furnace Models
Newer codes mandate that furnaces bring in combustion air
from the attic or from the outside instead of drawing the
combustion air from the conditioned space because drawing air
from the conditioned space is a waste of the expensive
conditioned air and creates oxygen depletion in the house.
Today, furnaces that have an efficiency rating of 90 percent or
more are called sealed or closed-combustion, direct vent, or
condensing. These bring combustion air to the appliance via
Polyvinyl chloride (PVC) piping from outside the building
envelope and use the same piping to vent the flue gases
outside. A closed-combustion heating system uses only outside
air for combustion and vents combustion gases directly
outdoors. Such systems are less likely to back draft and
negatively affect indoor air quality. Indoor air quality is
discussed in Module 8. A weatherization service provider can
use a TIF gas detector to check for the presence of combustible
gas indoors. A TIF gas detector is a device used to detect the

7. presence of combustible gas.
A condensing furnace extracts so much of the available heat
content from a combusted fuel that the moisture in the
combustion gases condenses before it leaves the furnace. This
furnace also circulates a liquid to cool the furnace’s heat
exchanger. The heated liquid may circulate through a liquid-to-
air heat exchanger to warm room air, or it may circulate through
a coil inside a separate indirect-fired water heater.
Another type of combustion appliance is called a package unit,
which combines the furnace, the coil, and the condenser in one
package. Package units are normally placed on the ground or
roof outside the structure. A condenser is the device in an air
conditioner or heat pump in which the refrigerant condenses
from a gas to a liquid when it is depressurized or cooled.
The outdoor component of an air conditioner.
An identifying feature of a 90%+ furnace is a condensate line
from the heat exchanger. All combustion processes in a 90%+
furnace are completely separate from the home’s environment.
As a forced air distribution device, the furnace has a return
plenum on the end of the furnace near the fan and a supply
plenum on the end of the furnace where the coil is attached in
areas where air conditioning is used. The highest operating
pressures are normally in the supply plenum as air is forced into
the plenum to be dispersed to the house.
Heat Pumps
Heat pumps are used in electric heating and are very efficient
because, instead of converting energy from one form to another
as in the combustion of natural gas, they move heat from one
location to another.
There are three types of heat pumps: air-source heat pumps,
ground-source heat pumps, and water-source heat pumps. An
air-source heat pump transfers heat from outdoor air to indoor
air during the heating season and works in reverse during the
cooling season. Air-source heat pumps are normally at least
150 percent efficient and use heat from the exterior air as the

8. source for heating a home. Some air-source heat pumps have
electric strip heating as a backup in areas that have extremely
cold weather.
Ground- and water-source heat pumps are referred to as
geothermal systems and can be at least 400 percent efficient.
The heat provided for the structure is taken from the ground
through a piping system that is located in wells or trenches for a
ground-source system and in a lake or pond for a water-source
system.
A heat pump can be easily differentiated from a combustion
furnace because a heat pump does not have a flue or any type of
water or fuel lines. The outdoor compressor runs during the
heating season when a heat pump is installed.
Unvented Combustion Appliances
Current building codes allow for the installation of unvented
gas fireplaces in homes. Old gas wall heaters installed in
bathrooms and some floor furnaces were also unvented. If a gas
stove top is used without the exhaust fan or if there is a
recirculating fan over the stove, this is also considered
unvented.
Whenever the HVAC equipment is included in an unvented attic
assembly, or an older atmospheric draft heater is being
replaced, the weatherization service provider should install a
sealed combustion unit.
Combustion Problems
When weatherizing a home, the weatherization service provider
should be able to visually identify any possible problems related
to combustion appliances. Furnaces, water heaters, and some
space heaters are subject to these areas of concern.
The primary danger is the introduction of carbon monoxide into
the living space. One problem with unvented appliances is that
there is always some carbon monoxide associated with the
combustion process even when the unit is operating at maximum
efficiency. Rusting or water streaking, chalky white powder
residue or visible rust, or stains on vents and chimneys can be
indications of the presence of carbon monoxide.

9. Back drafting is a condition produced when a house is operating
under negative pressure as a whole or in the combustion
appliance zone. The combustion appliance zone is the area
where the combustion appliances are located. Instead of the
flue gases exhausting to the outside, the negative pressure in the
house will pull the flue gases back into the conditioned space.
This can happen with as little as 3 to 5 Pascals of negative
pressure in the house when compared to the outside. If the pilot
light of a furnace or other gas-fired equipment keeps going out,
this can be an indication of back drafting.
Flame rollout, which is sometimes referred to as spillage,
occurs under the same conditions as back drafting except under
higher negative pressures, such as between 6 and 10 Pascals.
As the fuel ignites at the beginning of the combustion cycle,
there is sufficient negative pressure for the flame to be pulled
outside the combustion chamber and onto the surface of the
appliance cabinet. Soot markings, burned paint, or heat stressed
metal can be indications of flame rollout.
Another problem with combustion appliances is the chance that
the flue may be blocked. If generated smoke from a diagnostic
smoke machine, incense, or kitchen match does not enter the
draft diverter during operation, this may be an indication of a
blocked chimney or flue. A diagnostic smoke machine uses
dyed smoke vapor to aid in the detection and location of leaks.
Another primary problem with unvented appliances is the
introduction of water vapor to the indoor environment. This is
the main problem when the appliance is in excellent working
order.
If the weatherization service provider notices any of these
conditions, he or she should notify the homeowner of the danger
and encourage him or her to seek a professional’s advice.
Hydronic Systems
Sometimes hydronic heating systems are used to heat houses
because they contribute to conservation. Hydronic heating
systems pipe hot water to each room to warm the air by piping
the water through pipes in the floor, radiators, or other heat

10. distributing devices. Water makes a good convector because it
is inexpensive, available, easily replaced, and can hold large
amounts of heat.
As with all heating systems, the operation begins when the
thermostat is turned to heat. If water in the boiler is cold, this
causes the boiler’s burner to fire and the water in the system to
begin heating. As soon as the water temperature exceeds
ambient conditions, the circulation pump begins to move the
water through the system. This causes the cool water to return
to the boiler for heating. When the thermostat temperature is
reached, the burner shuts off. However, the circulating pump
continues as long as the water in the system is above the
demanded temperature. When the water temperature drops far
enough, the circulation system shuts down.
A weatherization service provider should examine the hydronic
system to make sure there are no leaks in the pipes.
Cooling Equipment
In addition to heating systems, most homes have air
conditioning components. Air conditioners are installed in most
of the eight climate zones throughout the United States. An air
conditioner is a device for conditioning air in an interior space.
A traditional furnace and air conditioner system, which is called
a split system, has three parts. Each part has its own nameplate
and model number. The air handler, or furnace, and the coil are
inside the house. The air handler provides for the circulation of
the air throughout the system and the coil is the part of the
system where the air is cooled. The coil is connected to the
condenser, which is the unit on the outside of the house. A
refrigerant circulates through the coil, outside to the condenser,
and back. As the air crosses over the coil, heat and humidity
are removed and then the cooled, dehumidified air is dispersed
throughout the house.
Air Conditioning Equipment Sizing
During the cooling season there are four basic areas of heat
gain: solar, internal generation, air leakage, and heat
transmission through the building shell. Heat gain is the

11. amount of heat that is introduced to a space from all heat-
producing sources.
Correct sizing of air conditioning equipment to counter heat
gain is very important for the comfort of a home’s occupants.
Many installations today are between 30 and 100 percent
oversized. Oversizing increases the operation costs due to short
cycling. In addition, the unit does not start the
dehumidification process until after it has been running for 12-
15 minutes. Therefore, it does not provide the proper
dehumidification for homeowner comfort. A correctly sized air
conditioner should run almost all afternoon (100 percent)
without cycling off on a hot summer day at design temperature.
A weatherization service provider who recommends replacing a
home’s HVAC system can perform load calculations according
to Manual J, Version 8 by taking the four areas of heat gain and
the home’s components into account. He or she can input the
data into a software program, which then predicts the amount of
cooling BTUs needed for the house. The provider can use this
estimate to select a new, more efficient HVAC system for a
home.
Air conditioners, or condensers, are sized in tons. There are
12,000 BTUH of cooling capacity per ton of air conditioning.
Therefore, a 3-ton unit supplies approximately 36,000 BTUH of
cooling to a house. Additionally, each ton of air supplies an
estimated 400 cfm (cubic feet per minute) of air.
Efficiency Rating Systems for Heat and Air Systems
All types and parts of heat and air systems are rated for
efficiency. All combustion furnaces, boilers, and room heaters
are rated in a laboratory and labeled according to Annual Fuel
Utilization Efficiency (AFUE). The AFUE is the measure of the
seasonal or annual efficiency of a residential heating furnace or
boiler. It takes into account the cyclic on/off operation and
associated energy losses of the heating unit as it responds to
changes in the load, losses of fuel-burning, chimney losses,
cycling losses, and heat loss as a result of the heater’s cabinet.

12. The AFUE does not consider the distribution losses from the
duct system. A duct is a round or rectangular tube that is
located in a wall, floor, or ceiling and distributes heated or
cooled air in buildings. Ducts may be constructed of flex duct,
thin gauge metal, duct board, sheet metal, fiberglass board,
flexible plastic-and-wire composite, or building cavities.
Heat pumps are rated either by the Coefficient of Performance
(COP) or the Heating Seasonal Performance Factor (HSPF).
The coefficient of performance is a comparison of the efficiency
of a heat pump relative to electrical resistance heating. The
heating seasonal performance factor determines heat pump
efficiency by using the ratio of heat moved in BTUs to the
amount of electricity used.
The air conditioners of both a traditional split system and a heat
pump are rated by the Seasonal Energy Efficiency Ratio
(SEER). The SEER is determined by dividing the amount of
heat removed from the conditioned space by the number of
watts of electricity used.
Efficiencies of existing equipment can be estimated by using
default equipment charts such as the one found on pages 3-33 of
the RESNET 2006 Mortgage Industry National Home Energy
Rating System Standards. There are other organizations that
also provide information on equipment efficiencies. Gas and oil
furnace, air conditioner, and heat pump data for older
equipment can be found in the Preston’s Guide. Visit the
Residential Energy Services Network (RESNET) or the Air-
Conditioning, Heating, and Refrigeration Institute (AHRI)
website for more information.
Duct Leakage
An unsealed duct can dramatically affect the operating
pressures of a building when the ducts are located outside the
conditioned space.
When there is a prevalence of leakage in the supply system,
more air is being pulled from the house by the return side of the
HVAC system than is being returned to the house. Duct leakage
of 25 percent in a four-ton HVAC system needs one ton of air

13. conditioning just to offset the duct leakage.
This situation causes the house to operate under negative
pressure when compared to outside. Negative pressure in the
house can cause such problems as the introduction of sewer, soil
gases, and moisture into the house, along with the possibility of
back drafting or flame roll-out, which is also known as
spillage. Duct leakage can also cause the introduction of
particulates from the attic, crawlspace, or basement into the
living space of the house.
If the primary leakage is in the return system, more air is being
supplied to the house through the supply system than is being
removed by the return system and the house operates under
positive pressure. Small amounts of positive pressure are
acceptable in hot humid and mixed humid climates, but can
cause severe damage to exterior walls in a cold climate due to
the possibility of condensation in wall cavities and subsequent
deterioration of wall components.
Leakage Testing
The weatherization service provider can test the ducts for leaks
by using various testing devices that are often called duct
blowers. A duct blower is basically a fan housed in a casing.
The duct blower test is used to measure the duct leakage of the
system in cubic feet per minute. A duct blaster® with digital
manometer is a device that is made of a small fan and a
manometer that is used to pressurize a duct system and measure
any air leaks in the ductwork.
The testing device is attached to the duct system usually at the
largest return closest to the unit. The remaining supply
registers and return grills are sealed with register tape, which is
an 8-inch wide piece of plastic with an adhesive on one side.
The system is then pressurized by the testing device to a
standard pressure of 25 Pa in relation to the house. Once
pressurized, the weatherization service provider determines the
amount of leakage based on the amount of air that goes through
the fan. A weatherization service provider may use a flow hood
to measure the air flow at a register in an HVAC system.

14. Two types of leakage are measured: total leakage and leakage
to outside. Total leakage refers to the leakage from the duct
system both into and outside of the conditioned space. Leakage
to outside testing is performed in conjunction with a blower
door and only measures the leakage from the duct system
outside the conditioned space. The leakage to outside test is the
more important of the two tests.
An exhaust flow pan measures flows of items such as exhaust
fans and outdoor air ventilation systems to verify that these
items meet industry standards. A weatherization service
provider may use a flow plate to test a specific span of the duct
system. A flow plate, which is sometimes called a damper, is a
device used to stop or control the air flow inside a duct.
Duct Leakage Subtraction Method
One way to obtain a rough estimate of duct leakage is to use the
duct leakage subtraction method. This method includes
performing two blower door tests: one under normal conditions
and the second with the duct system covered. The difference in
the airflow measured by the blower door is an estimate of the
duct system leakage.
Pressure Pan Testing
A pressure pan is a device used to approximate duct leakage at
each register. The weatherization service provider runs the
blower door at a normal pressure difference (also known as
Delta P or ΔP) of 50 Pa, and places the pressure pan, which is
attached to a manometer, over a supply register or supply grill.
A well-sealed duct run should have a very low reading of less
than 1 Pa. Higher numbers indicate more duct leakage. This
method, though not very accurate, can help determine where the
primary leaks in a duct system are located.
Tracer Gas Testing
Tracer gas testing is the most accurate means of measuring the
air change rate that occurs naturally during normal house
operations combined with differing weather conditions. House
pressures change based on HVAC equipment, exhaust fan
operation, and existing stack and wind pressures. The tracer

15. gas measures the induced air leakage under these normally
operating conditions. To perform a tracer gas test, a
weatherization service provider releases an inert gas such as
sulphur hexafluoride, carbon dioxide, or perflourocarbon into
the air of a building.
Over a period of several hours, the provider takes air samples.
These samples are sent to a lab for analysis using a gas
analyzer. The concentration of the inert gas is measured over
time and the natural air change rate can then be predicted with a
high level of accuracy. The time and expense of this process
make it impractical for anything but research or for the
diagnosis of health problems in large buildings.
Duct Sealing
Once the weatherization service provider has found the leaks in
a duct system, it is time to seal the ducts. A sealed duct system
adds to the overall operating efficiency of the HVAC system by
improving the airtightness of the house. In addition, a sealed
system minimizes potential negative problems due to pressure
changes in the house. This creates a more comfortable and
healthy environment. Last, sealing a duct system results in
significant energy cost savings.
When examining the system for areas that need sealing, all
areas must be inspected, not just the unit itself. A visual
inspection of the duct system is often sufficient to determine if
sealing has been performed. The presence of duct tape and the
lack of mastic or code-approved tape is a good indicator that the
duct system is unsealed and that sealing is needed. One of the
areas that is most often left unsealed is the area between the
supply boots, the return boxes, and the drywall. Substantial
leakage can occur in this area.
Sealing the duct system should be a high priority at any point
where the ducts are located outside the conditioned space.
Sealing Methods
The best way to seal a duct system is to use duct mastic. Mastic
is a non-toxic, spreadable paint-on, putty-type adhesive-sealant
used for permanently sealing the fabricated joints and seams of

16. sheet metal air ducts, rigid fiberglass air ducts (UL-181 listed),
flexible air ducts (UL-181 listed), and thermal insulation. It
comes in one and two gallon plastic buckets and has the
consistency of dense toothpaste. There are two types of mastic:
one with fibers and one without fibers. The duct mastics
containing fibers are the more resilient of the two.
Mastic can be applied using a paintbrush, a flat tool such as a
putty knife, or a gloved hand. All metal folds, joints, and seams
in metal ductwork and on the unit itself should be covered with
the material. The start collars should be covered where they are
screwed onto the plenums. Insulation may be found either on
the exterior or the interior of the supply plenum. If the sound is
dull when the weatherization service provider thumps on the
metal of the supply plenum, it is an indicator that the insulation
is on the interior of the plenum.
When using flex duct, the provider should apply the mastic to
the start collar. Then he or she should pull the duct’s inner
liner onto the start collar and attach it with a nylon tie. Next,
the provider should place the outer insulation and radiant
barrier portions of the flex duct tight against the boot or start
collar and apply more mastic. This step will prevent warm,
moist air from entering between the inner liner and insulation,
condensing, and forming pools of water in the insulation, which
will result in decreased insulation R-value. Should this
situation occur at a home, a colder temperature and the weight
of the water can be detected by feeling the insulation.
When a building cavity, which is also called a chase, is used as
part of the duct system, this may be the location of the largest
air leak in the duct system. Correcting an air leak in a building
cavity usually requires removal of drywall or other house
components.
The weatherization service provider should seal as many air
leakage sites as possible in the ceiling plane, vented crawlspace,
or unconditioned basement of the house. Finding many of these

17. leakage sites will involve moving or removing existing
insulation.
Required Videos:
The structure’s heating and cooling systems play a vital role in
conditioning the indoor air for temperature control measures
during the many seasonal changes that take place throughout the
calendar year. By utilizing the laws of thermodynamics, an
individual can design a functioning HVAC system that is sized
to meet the heating and cooling requirements in order to
maintain a quality of life for the structure’s occupants. It is
very important that we size our heating and cooling equipment
based on the living space that is required to be conditioned for
the occupants’ overall comfort. An oversized HVAC unit will
provide too much conditioned air and an undersized system will
have to work much harder to maintain the temperature settings
established by the structure’s occupants. By sizing our units
correctly based on the information provided within this module,
an individual can correctly size the HVAC system based on the
livable floor space area to be conditioned in order to maintain
the comfort levels for the occupants during seasonal changes.
The following YouTube video presentations will provide you
with valuable information on sizing HVAC systems based on
the floor area that is required to be conditioned for the
occupants’ maximum comfort.
Psychometric chart simplified
Understanding HVAC
How a furnace works and how to keep it energy efficient
Gas furnace basics – Part 1
Gas furnace basics – Part 2
Gas furnace basics – Part 3
Gas furnace basics – Part 4
Air conditioner maintenance
HVAC Right-Sizing Part 3: Air Distribution & Duct Design
Required Presentations:
Why we work on heating systems
Heating system efficiency rating

18. Introduction to heating system sizing
Venting systems
Distribution systems
[INSERT TITLE HERE] 1
Running head: [INSERT TITLE HERE]
[INSERT TITLE HERE]
Student Name
Allied American University
Author Note
This paper was prepared for [INSERT COURSE NAME],
[INSERT COURSE ASSIGNMENT] taught by [INSERT
INSTRUCTOR’S NAME].
Directions: Please provide a response to each of the following
questions using APA guidelines for formatting and citations.
Each response must be at least one paragraph in length

19. consisting of three to five sentences.
1. Name the four factors that contribute to a person’s comfort
in an environment.
2. Describe relative humidity and mean radiant temperature.
3. How does the dew point affect condensation?
4. Describe the three types of heat movement.
5. Name types of heating systems.
6. What is a furnace? What are its basic components?
7. What are some characteristics of older furnace models?
8. What are the parts of a traditional furnace and air
conditioner system?
9. Describe various tests that can be used to detect leaks in
the duct system.
10. What is the best way to seal leaks in ducts?