Energy is being lost unnecessarily in homes through heating and air-conditioning duct leaks resulting from deterioration or improper installation. By correcting these problems you can save tremendous energy losses.

You can see in the image to the right, the ductwork is leaking heat around the joints into the unconditioned basement of this 1979 home. Ducts that pass through unconditioned spaces, attics, garages, or crawl spaces, have a good chance of losing energy. Losses can be very high if the ducts are uninsulated. Even when the ducts are wrapped with insulation, leaks at joints and corners can be big energy losers. Leaks in supply ducts lose heated or cooled (conditioned) air to the attic or crawl space or between floors before the air can be delivered inside the house, wasting energy.

If the return ducts in the heating and air-conditioning system have holes, they can draw in attic air as hot as 130°F or outside air as cold as 0°F. As a result, the system must work harder and use more energy to heat and cool the inside of the house to the desired temperature.

Energy is also lost because differences in air pressure result from leaks in supply-and-return ducts. Air escaping from leaks in supply ducts must be replaced with air from outside the house, which is often much warmer or cooler than the conditioned air. Additional energy is needed to condition the replacement air.

The seal between the air conditioner and the metal supply-and-return ducts often fails on rooftop-mounted units because the sealant material deteriorates after long-term exposure to ambient temperatures and the sun. Also, the air conditioner pulls away from the ducts as it settles on its mounting supports.

Some HVAC contractors seal duct joints with duct tape, which is often used improperly and which deteriorates. We recommend connecting and sealing ducts with mechanical fasteners, mastic, not duct tape. Duct Mastic is a caulking material that can be applied simply with a disposable glove.

Another problem that many HVAC contractors are not aware of, is that the house often serves inappropriately as a duct. Many home HVAC systems are in interior closets or have return plenums built under stair wells. Use of closets and other parts of the house as a return duct can draw air from the attic or crawl space because of pressure differences. The solution is to use ductwork for all supply and return ducts. You can also reach into the ducts from the vent side to capture the connection that usually fails first if not appropriately secured with sheet metal screws by the builder. During our inspections, this seems to be one of the places where ducting fails more frequently.

To improve energy efficiency for an existing home, thermal images from an energy house inspection or home energy audit will reveal many of the leaks in the ductwork behind walls. After the review you will have a roadmap to proper weatherization. Whether you are the do it yourself, "DYI" person or want to hand off to a contractor or handyman, the roadmap will help you make the best decision first. Fixing whats found will greatly improve your comfort, savings and reduce your carbon footprint.

Resouce Cited: Oak Ridge National Laboratory, the science and technology laboratory managed for the U.S. Department of Energy