Sealing leaky ducts can help improve comfort and avoid indoor air pollution problems, fire hazards, and rooftop ice-dam formation during the winter.

Having your ducts professionally sealed to reduce leakage can help avoid a number of problems, in addition to cutting back on your energy bills. Well-sealed ducts can:

• Well-sealed ducts have been shown to improve the flow and temperature of the air delivered to rooms, improving the comfort of even those rooms that were previously uncomfortable during certain times of the year.
• Reduce moisture damage or mold in the spaces surrounding the ducts (such as the walls, floor, or attic). For ducts located in the attic, moisture and heat leaks through the ducts can result in condensation on the attic walls or ceiling, or in the winter can cause rooftop snow to melt and form dangerous ice dams. Ice dams are a common cause of roof damage and also create dangerous conditions for pedestrians around the home.
• Reduce phenomena such as door slamming. Leaky supply ducts can cause a situation called "depressurization", in which the house experiences a kind of suction effect because the amount of air being exhausted from the home is greater than the amount being supplied. One symptom of depressurization is doors that mysteriously slam.
• Reduce fire risk. Depressurization in rooms containing combustion appliances (such as water heaters or furnaces) can cause the burner flames from those appliances to come into contact with flammable parts of your home. This phenomenon is called "flame roll-out" and is a known cause of house fires. Homes will well-sealed ducts are less prone to flame roll-out.
• Help avoid indoor air pollution problems. Depressurization in rooms containing combustion appliances can also cause dangerous combustion products (fumes), such as carbon monoxide, to be pulled into the home. Depressurization can also increase the rate of radon http://www.stat.columbia.edu/radon/ entry into a home, particularly in basements.
• Help reduce odors, dust and mold in the air circulating through your ducts. Leaky return ducts can cause basement or garage odors, crawlspace dust or mold, or attic insulation fibers to be sucked into your duct system and then delivered into your rooms. Not only is this detrimental to your health, but these particles can also degrade the performance of your air conditioner by clogging up the cooling coil.