Duct Sealing

Sealing leaks in your heating and air conditioning duct system can be one of the most effective energy improvements to your home. Duct sealing and repair can provide an opportunity for significant energy and cost savings, while also improving comfort.

Ducts and duct systems have two very specific purposes. During the winter months, duct systems supply heated air throughout the home through supply ducts and return cooler air through return ducts for filtering and reheating. In the summer, duct systems supply cooled air throughout the home and return warmer air for filtering, moisture removal, and recooling.

Holes in your ducts allow air to escape from or enter your duct system, increasing your energy costs. Leaks in supply air ducts will waste energy by forcing heated or cooled air into unconditioned areas such as crawl spaces or attics. Leaks in the return air ducts have the opposite effect. These leaks allow unconditioned air from those same spaces to enter the duct system. Duct systems are often hidden from view, which makes finding leaks difficult. Fortunately there are ways to test and repair ducts to improve the energy efficiency of your home.

What Is Duct Sealing?

Duct sealing is the process of identifying and repairing holes in the home's duct system. The standard repair procedure starts with a visual home inspection. This is followed by a duct pressurization test, which should be conducted by a qualified heating and air conditioning contractor or testing organization. This test, often called a "duct blaster" or "blower door" test, identifies the amount of air leakage in your duct system and where it is occurring. Common leakage sites are around air registers and grilles, duct connections, panned floor joists, and the heating and air conditioning unit itself.

Repairs to ducts are made using a special adhesive called "mastic". Mastic is applied over a mesh tape to form a seal over gaps in the ducts. This seal will last for many years, unlike old-fashioned cloth duct tape. Other acceptable methods include: silicone caulk, duct sealer, and special foil tape. Duct sealer is available in cans and caulk tubes. Check the label, and purchase a sealant that is nontoxic. New improved foil tapes have better adhesive and cold weather characteristics than before. Follow the manufacturer's recommendations and make sure ducts are dirt-free before applying any type of foil tape. Once repairs are made, a second "duct blaster" or "blower door" test should be conducted to confirm the reduced air leakage.

Caution: Duct repairs attempted by untrained personnel can have an adverse effect on the home's occupants. Anyone repairing duct leaks and duct systems should be experienced and familiar with how duct modifications can affect living conditions and air quality.

Benefits

As a homeowner, you can benefit from repairing duct leaks in the following ways:

• lower heating and cooling bills
• improved humidity control
• increased comfort
• improved indoor air quality
• improved equipment efficiency