A: Two things: 1) You can give your
heating system a tune-up. If you have an air conditioner or a heat pump
the technician should check the freon charge in your system. If you have
a gas furnace the technician will clean and check the heat exchanger for
safety. 2) You can seal the leaks in your ducts. This means sealing up
all the holes where heated or cooled air can leak into unconditioned spaces
- attics, basements, or wall cavities. You should be warned, however, because
there are potential problems if the sealing is not done properly.
Q: Should I have my ducts cleaned?
A: Duct cleaning can be useful in
some circumstances, but the real answer is to keep dirt out of the ducts
in the first place. That means making sure that you have a filter on the
return side of your system - either at the return grille or near the furnace,
where the return duct enters the air handler. The filter should be changed
every 4-6 months, or when it gets dirty. Making sure that your air filter
is clean will also improve the performance of your system overall. If the
filter is very dirty the system may be compromised because the fan cannot
pull the correct amount of air through the system.
Q: I have a gravity heating system. Should I replace it because it is old and inefficient?
A: Not necessarily -- there are
trade-offs. The combustion efficiency of a modern furnace is about 80%.
Gravity furnaces have a lower combustion efficiency. However, they are
quite reliable because they have very few moving parts. Also, the duct
systems connected to gravity furnaces generally have fewer losses than
those connected to forced air furnaces because the air in the duct is at
a lower pressure. The ducts are generally larger (lower resistance) so
that the lower pressure air can make it to the living space. If you do
decide to switch the furnace, but retain the same duct system, the airflow
to the living space will generally be very high because of the low resistance
of the ductwork.
Q: Is it true that forced air distribution systems make the house drier in the winter?
A: Possibly, but not necessarily.
Forced air distributions systems only make the house drier if they are
not working properly. If there are large leaks in the return ductwork then
dry outside winter air will be drawn into the house through those leaks.
This will tend to dry the air in the house. Conversely, hot water systems
that are not working properly sometimes add moisture to the house. Steam
or hot water systems usually have a pressure relief valve which releases
moisture to the room when the pressure in the system gets too high. The
main reason for houses being dry in the winter is building envelope leakage.
Warm indoor air leaks out through holes in the attic plane, and is replaced
by cold outside air leaking in at the floor. This cold air is dry compared
to the warm air that was lost. The colder it gets outside, the more air
leaks out of those holes.
Q: The ducts in my basement are wrapped with asbestos. Should I have the asbestos removed?
A: Asbestos is harmless as long
as it is not airborne. It causes a problem because it forms very small
particles, which travel fairly deep into the lungs if they are inhaled.
Asbestos can be removed by a professional or it can be covered with an
impermiable surface which prohibits the particles from becoming airborne.
(Generally the particles do not become airborne unless they are disturbed.)
If you have any concerns about asbestos consult a professional.
Q: I have heard that duct tape should not be used to seal ducts. What materials should be used?
A: The products that should be used
to seal ducts are mastic, butyl tape, foil tape, other heat approved tapes,
basically, anything except duct tape.
Q: My ducts are located in the basement. Should I insulate the ducts? Should I insulate my basement ceiling?
A:This is a difficult question because
each case is different. If the basement is conditioned then the basement
ceiling does not need to be insulated, however, the ducts should still
be insulated (so that they deliver their heat to the space where it is
supposed to go.) In general, if the basement is unconditioned then the
basement ceiling and the ducts should be insulated. One possibility is
to insulate them together. Fiberglass insulation can be installed between
the joist bays underneath the ducts, thus the ducts are on the "warm" side
of the insulation, although they are still located in the basement. The
fiberglass should be held in place by netting or insulation supports. Another
option is to use what is called a BIB system - blown in cellulose insulation.
A contractor will install a membrane on the bottom of the floor joists,
and then will fill each joist bay with blown in cellulose.
Q: Why is it so much hotter on the second floor of my house than the first floor when the central air conditioner is running?
A: There are several reasons: First, there is usually more load upstairs. Heat conduction through the ceiling and solar gain from skylights add significantly to the cooling load of a house. The radiation from a warm ceiling also adds to the load. (the ceiling of the second floor heats up due to conduction from the attic space as well as radiation from the attic roof. Second, the cooling system is generally not designed to meet the higher loads on the second floor. Often cool air delivery is calculated based on room size rather than load. A third possible reason for the upstairs of a house being hotter than downstairs during the cooling season is that the cold air return may be located on the first floor. The warm air on the second floor may not be making its way into the air handler to get cooled. The situation can be exacerbated by thermal stratification (because heat rises) before the system turns on, meaning the upstairs is hotter to start with. Zone controls can help to alleviate the problem, as can proper duct sizing according to loads.
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