Straight Talk Articles

Is Your Ductwork Delivering?
August, 2016

Dear Pat: I moved from a home with wall heaters to one with a central heating and air conditioning system and a duct system. What should I be doing to make sure my ducts are working efficiently? – Carla

Dear Carla: Homes with central forced-air heating and cooling systems, like furnaces, central air conditioners, and heat pumps, use air ducts to deliver the conditioned (heated or cooled) air through the home. Ducts are often concealed in walls or in areas of your home you don’t go to often, like your crawlspace, so many people do not immediately think of them as an area to save energy.

You may have received flyers in the mail with offers for air duct cleaning and claims that doing so will improve the air quality and efficiency of your home. However, duct cleaning may not always be necessary for air quality, and there is no indication that just cleaning your air ducts will improve your system’s efficiency.

Duct cleaning may be needed if:

  • There is visible mold in your duct system or there was a recent flood that caused mold or mildew in your home.

  • There is something in the ductwork impeding airflow, like debris or an infestation. Major renovations or new construction can put construction debris into the duct system, so after construction is a time to consider duct cleaning.

  • Your heating registers are releasing dust into the air.

  • Home residents have allergies or asthma problems that have not been alleviated by other changes.


While duct cleaning may not always be needed, regularly changing your air filters can help your heating and cooling system work more efficiently. How often you change them depends on how much your system runs, whether you have pets, and whether you periodically vacuum your air filters. An average home should change their air filters four to six times a year.

Though duct cleaning may not do much for the efficiency of your systems, duct sealing is important for saving energy and utility costs, particularly if your ducts are in unconditioned spaces, like a crawlspace or an uninsulated attic. In the typical home, 20-30% of heated or cooled air leaks out through the gaps, holes, and disconnections in the duct system, which can cost you money and make your home less comfortable. You wouldn’t put up a with a leaking water pipe, so why should you put up with a leaking air duct?

The best way to assess the condition of ductwork is to have it tested by a  professional home energy auditor who can conduct a Duct Blaster test. If you can easily access your ducts, you might get by with just a visual inspection, which will identify the larger holes and disconnections. Where ducts meet each other or where they connect to a heating register are common places to find duct leaks. A professional trained in ductwork can help you identify and fix the gaps and leaks you may not be able to see. Talk to your co-op, energy auditors, or a local HVAC contractor to find a person to help.

Once gaps and leaks have been identified, you can work to seal your ducts. Small duct leaks can be sealed with mastic, a type of caulk. Larger duct leaks and disconnections may required additional lengths of duct, mechanical fasteners, or special heat-resistant tape. Don’t use duct tape—ironically, it is not designed to adhere well to ducts.

If you have ducts in unconditioned areas, like an attic or crawlspace, your ducts could be wasting energy by heating or cooling the surrounding air, even if there are no leaks in the ductwork. Insulation around the ducts can help reduce this energy loss. Consider also adding insulation in the unconditioned space, such as in the attic or basement, which can further increase the efficiency and comfort of your home.

This column is from the August issue of Straight Talk, which is a service of the National Rural Electric Cooperative Association to its member co-ops.  Straight Talk is distributed by electric co-ops around the country as part of a monthly print publication or on co-op websites.

For more information on duct testing and sealing, see this page with more resources. 

Regularly vacuuming your air filters can extend their life and help your heating system work more efficiently. Photo Credit: Janwikifoto

Mastic can be used to seal small gaps and leaks in your ductwork. Photo Credit: Weatherization Assistance Program