Ducts carry air from the central heater or air conditioner to each part of the home and back again. Unfortunately, ducts can waste a significant amount of energy and money due to improper installation and poor materials. A number of factors can affect the functioning of ducts, including:
Duct Sealing
Typically, ducts are so leaky that more than 35% of the conditioned air is lost before it arrives at the target room the duct is trying to reach. This means that more than 20% of the energy used to condition the air is wasted. Improved duct performance depends on sealing the seams between the ducts. Duct tape, which is commonly used, does not adequately seal the joints nor does it last very long. UL listed tapes or duct mastic should be used to seal all joints and seams in the ductwork.
Duct Location
Builders often place ducts in spaces that homeowners do not heat or cool, such as attics, crawlspaces, garages, or unfinished basements. The extreme temperatures that can occur in these spaces (attic air in the summer can reach above 150F) will affect the temperature of the air moving through the ducts into the home. Installing ducts within the conditioned area of a home will substantially reduce duct air losses.
Duct Insulation
As air moves through uninsulated ducts, its temperature is affected by the temperature of the hot or cool space where the duct is located. To reduce these temperature variations, ducts need to be insulated. If the ducts are located in the living area of the home, which tends to remain at a reasonable temperature, then the need for insulation is reduced. However, some insulation is still needed to ensure that the conditioned air is delivered at the desired temperature and to prevent condensation on the duct walls.
Duct Sizing
Ducts that are not properly sized and designed can result in poor air distribution, unhealthy indoor air, discomfort, increased noise, and higher utility bills. The best ducts are properly sized, run minimally, have smooth interior surfaces, and the least number of direction and size changes. If the home has tight construction, increased insulation, and advanced windows, the expense of running ducts to the perimeter of the home is not necessary, since there will be less variation in temperature throughout the home.
Tightly sealed ducts can offer you:
- More consistent comfort - the proper amount of conditioned air distributes to each room.
- Significantly improved indoor air quality - reduces intake of dust, pollen, and other pollutants from unconditioned spaces.
- Lower utility bills - reduces the amount of conditioned air needed to heat and cool your home.
In typical American homes, ducts leak 20-30% of the air being forced through them. This means money is being wasted when heating or cooling your home. Duct systems should be properly sealed and verified by a field test to reduce any leaks.
View these duct-related fact sheets to learn more detailed information.
If you own an existing home, find out about properly sealing your duct system.
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