Fixit: For greatest efficiency, seal ducts before insulating them

Q I recently read that air ducts in a home should be insulated to conserve energy. What does that mean? How is that done in an existing home? Are there specific companies that do this work?

A Ducts can be insulated with oversized batt insulation. You can do it yourself or hire a heating and air-conditioning contractor to do it for you. However, it's not the first step to take. To save energy and to improve the distribution of heated or cooled air in your home, you need to seal the air ducts first.

To do that, use either a brush-on mastic or a metallic tape with a UL Listing for the UL Standard 181. Make sure to seal all seams, joints and penetrations in the ducting. It's best to focus on the return ducting, because that's where most leaks occur. Then follow with all ducts that are accessible.

If your basement is finished and you have no access to the ducting, consider hiring a contractor who can seal all of the ducting in the house from the furnace area. Researchers at Lawrence Berkeley National Laboratory (a U.S. Department of Energy lab) developed a technology to do that and it is available under the brand name Aeroseal. The technology can provide real energy savings and increased comfort (for more information, see www.aeroseal.com).

Once ducts are sealed to your satisfaction, insulation can be applied directly to exposed ducts, such as those in the basement ceiling. You can do that yourself, too, with an "oversized" fiberglass batt. The batt has an exterior foil facing with a heavy-duty nylon web reinforcement for durable performance. The batt may be from 3 to 4 feet wide, 2 to 4 inches deep, and as long as 50 feet.

If you have ducting in attic areas, it's recommended that you insulate it to the same level as the attic area, with an R-44 rating as the minimum. This applies to ducting in unconditioned crawl spaces, as well.

Information from the Minnesota Office of Energy Security, St. Paul