Leaky ducts can reduce heating and cooling system efficiency by as much as 20 percent according to the E.P.A. Furthermore, leaky ducts can contaminate your indoor air with mold, dust and toxins that represent a serious health hazard. Sealing and insulating ducts can help with common comfort problems, such as rooms that are too hot in the summer or too cold in the winter. It can also alleviate indoor air pollution problems like the fumes from household and garden chemicals, insulation particles, and rodent and insect droppings being introduced into the home. These indoor air pollutants can enter your duct system, aggravating asthma and allergy problems. Sealing ducts and ensuring a healthy indoor fresh air exchange rate can help improve indoor air quality by reducing the risk of pollutants entering ducts and circulating through your home.