Should Air Conditioning Duct Work Be Insulated?

Function

• In a home, the air-conditioning ductwork usually runs through the attic or through crawl spaces under the house to deliver heated or cooled air. The ductwork also carries air back to the heater, air conditioner or HVAC system to be heated or cooled again. This network of ducts is made of flexible tubing, rigid rectangular or round metal ducts. When uninsulated ducts run through an attic or crawl space, they lose from 10 to 30 percent of the air through leaks, holes or other problems. Insulating the ducts reduces the energy used for heating and cooling.

Preparation

• Insulating ducts can be do-it-yourself or professional projects. The first step is inspecting the ductwork for holes, cracks and proper connections. Holes and cracks are repaired with mastic sealant, metal tape or other duct-specific sealing products. Despite its name, duct tape is not durable, making it a poor product for duct repair. If sections of sheet metal are loose, sheet metal screws are used to tighten the sections and reduce air leaks. Sometimes ductwork supported by wire hangers sags down and the sections come apart. Wasted air spews out of the open ducts and does not heat or cool the house. Check support wires and ensure all ducts are connected without crimped or collapsed sections.

Insulation

• Some states require insulated ductwork. If you are retrofitting a home with a new forced-air system, be sure flexible ductwork is insulated and metal ductwork meets or exceeds standards in your region. For existing ductwork, wrap the ducts with insulation batts or blankets. Check home centers for duct insulation that is easy to handle in cramped attics or crawl spaces. Use the highest-rated insulation, such as R-6 to R-11, that will fit in the confined space. Use faced insulation or vapor barrier insulation with the barrier installed outward away from the ducts. This inhibits condensation forming on the ducts and protects you from direct contact with the insulation.

Tips

• Sealing and insulating duct work improves indoor air quality by reducing contaminants that are drawn into cracked or leaking ducts. As forced air rushes through the ducts, it can pull in pollens, fumes and dust from outside the ducts. Leaking duct work can draw carbon monoxide from gas appliances, spreading fumes into the home and causing health problems. In addition, properly sealing and insulating the ducts helps reduce temperature hot and cold spots in the home to improve overall comfort.