Seal and Insulate Ductwork To Save

IF YOUR HOME’S DUCT WORK is outside of the building envelope, the system may be operating at decreased efficiency.

Ductwork is the array of ducts and pipes, usually made of sheet metal or fiberglass, that transports warm or cold air from your air conditioner or furnace throughout your house. The building envelope—the thermal barrier between the outside and inside—keeps the outside out and the inside in. When unsealed and uninsulated ductwork runs outside that envelope, such as through a crawlspace or attic, it can create leaks and lose warmth or cold.

An air leak from a duct in an uninsulated area could mean conditioned air is escaping to the outside. Lost air is then replaced by unconditioned air, increasing the heating or cooling load on the house. Plus, that unconditioned air might contain contaminates like dust or pollen, which affects the health of the people living inside.

Uninsulated ducts may deteriorate from condensation forming inside or outside the ducts. Adding insulation can reduce condensation while keeping warm or cold air in until it reaches its destination inside. Insulating ducts may help lower energy consumption and utility costs.

When ducts are outside the building envelope, specific codes determine the acceptable levels of airtightness and insulation of the ducts.

Minor duct repairs usually can be completed by the homeowner, but it may be necessary to hire a qualified professional to seal and insulate ducts in unconditioned spaces to ensure the job is done properly.

The Department of Energy offers the following tips for minor ductwork repairs:

Check your ducts for air leaks. First, look for sections that should be joined but have separated and then look for obvious holes.

Duct mastic is the preferred material for sealing ductwork seams and joints. It’s more durable than any available tape and generally easier for a do-it- yourself installation. Its only drawback is that it will not bridge gaps more than a quarter-inch. Such gaps must be first bridged with web-type drywall tape or a good quality tape approved for high temperatures.

If you use tape to seal your ducts, avoid cloth-backed, rubber adhesive duct tape, which tends to fail quickly. Instead use mastic, butyl tape, foil tape or other heat-approved tapes. Look for tape with the Underwriters Laboratories logo.

Water pipes and drains in unconditioned spaces, such as a crawlspace, attic or garage, could freeze and burst if the heat ducts are fully insulated because there would be no heat source to prevent the space from freezing in cold weather. However, using an electric heating tape wrap on the pipes can prevent this. Check with a professional contractor.

Be sure a well-sealed vapor barrier exists on the outside of the insulation on cooling ducts to prevent moisture condensation.

If you have a fuel-burning furnace, stove or other appliance or an attached garage, install a carbon monoxide monitor to alert you to harmful CO levels.

Be sure to get professional help when major changes to ductwork are needed.