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Frequently Asked Questions

Q: What can I do to improve the TED system at my house?

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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Last Modified: October 30, 2001