In many homes, the ducting runs in attics, crawl spaces and basements – where you don’t want your valuable “conditioned” air to leak out, or the polluted air to leak in. Sealing your duct system can not only reduce your utility costs, but it can improve the quality of air in your home and reduce dust accumulation.
Ductwork is usually made up of metal, flexible duct or ductboard (a fiberglass ducting product), and can have gaps or air leaks around the seams and connections. Taping the joints is usually only temporary, considering the extreme temperatures to which the ducting is sometimes exposed. Ducting can be sealed using “mastic” which resembles a thick, gooey paint-like substance.
Leaking ductwork can cause a whole host of problems. If the air you are heating or cooling leaks OUT of the ductwork on the supply (pressurized) side, you can lose up to 25% or more of the air you are paying to condition. Also, if your supply air is leaking out into an attic or crawlspace, that causes your house to go into a slightly “negative” pressure.
This negative pressure will pull air into your home wherever it can find it – back drafting down chimneys, pulling in contaminated air from crawlspaces and attics. If you have very fine dust that looks like the insulation in your attic, this could be the source. If the ductwork leaks on the return (suction) side of the system – you are actually drawing air into the system wherever this leaky ductwork is located – usually the crawlspace or attic. The same problems can occur with contaminants and excessive dust in your home.