Improving Ducts: Duct Sealing and Insulation

Ducts #1

Ducts before improvement (arrows show common leaks)

Ducts after improvement (arrows show proper air flow)

Ducts after improvement (arrows show proper air flow)

In the second installment of our seal and insulate series, ENERGY STAR Product Manager Doug Anderson gave advice on how to choose a contractor in order to seal air leaks and add insulation to your attic during the warm summer months. Today’s post goes one step further—giving expert advice on sealing ducts and adding duct insulation. Leaky ducts can reduce heating and cooling system efficiency by as much as 20 percent. Sealing and insulating ducts increases efficiency, lowers your energy bills, and can often pay for itself in energy savings.

By: Doug Anderson

In previous blog posts, we’ve talked about the benefits of air sealing and insulating your attic. In this post, we’ll address some topics that you may be less familiar with: sealing ducts and adding duct insulation.

In homes with forced-air central cooling, a system of ducts is used to deliver the cooled air to the rooms and other living spaces of the home. Unfortunately, in typical homes, the duct system can lose about 20-30% of the air that moves through due to leaks, holes, and poorly sealed connections. Addressing these issues by hiring a heating and cooling contractor or other residential energy efficiency professional can increase summer comfort, as well as save energy and money.

There are two types of ducts in most homes: supply ducts that deliver the cool air through registers or vents in each room, and return ducts that bring air back to your air conditioner. If your supply ducts are leaky, cool air from your air conditioner is wasted on its way into the living space; and leaky return ducts can result in dusty, humid, or moldy air being pulled into the system, which can aggravate allergies and other health issues.

Identify Problem Areas

The ducts that run through spaces like attics, crawlspaces, basements, and garages typically waste the most energy. You or your contractor can identify areas for improvement in your home by inspecting ducts in these areas for the following types of problems:

– Duct tape that is dried-out, loose, or has fallen away from duct joints

– Ducts that have been torn or crumpled

– Poorly hung ducts with bends and kinks that restrict air flow

– Ducts that are partially (or completely) disconnected

Next Steps

Mastic sealant is an effective way to stop leaks at duct joints

Mastic sealant is an effective way to stop leaks at duct joints

Metal tape can also be used to seal duct leaks

Metal tape can also be used to seal duct leaks

If you find these types of duct problems in your home, EPA recommends calling a professional to help you address them. A contractor will also be able to test air flow after the job is completed to make sure that your system is performing correctly.

In many areas, you can also find pre-screened, trained, and certified contractors through a locally-sponsored Home Performance with ENERGY STAR program. These programs are a great place to start looking for contractors to help you with your project. To find out if a program exists in your area, visit our website.

For some homeowners, sealing and insulating ducts can be a do-it-yourself project. If you choose to make these improvements on your own, be sure to have your heating and cooling contractor assess the system’s air flow when you are done to make sure any air sealing has not caused any air flow problems – and perform a combustion safety test to confirm there is no backdrafting of gas or oil burning appliances. To learn more about improving your home’s ducts, check out

About the Author: Doug Anderson is an ENERGY STAR Project Manager and has been with EPA for 14 years. He works on issues related to the home envelope, including insulation products and energy-efficient residential windows.


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