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Duct Sealing and Insulation

A heating or cooling system can only be as good as the ducts that carry the conditioned air through your home. Ducts are typically made of sheet metal, fiberglass, or other materials. They can lose energy in two ways, by conduction of heat through the material and by air leaking through cracks and seams.

Locating and Sealing Leaks

Testing ducts for leaks and pressure imbalances. Not sure how to tell if your ducts need some improving? You may want to call an energy professional to locate leaks and pressure imbalances. A professional will use diagnostics tools, such as a blower door, duct blaster, and digital manometer to identify leaks and imbalances. You can conduct a visual check of your ducts to look for holes or separated joints; however, ducts are often "hidden" under floors or in walls, which limits the effectiveness of visual inspections.

Seal duct leaks with fiberglass mesh and mastic Seal duct leaks with fiberglass mesh and mastic, mechanical fasteners, or foil tape, but do not use duct tape.

When to Insulate

Lack of proper insulation is a common and costly problem. Without insulation, ducts will leak heated air into spaces intended to be unheated, such as crawl spaces. If you find that your ducts are uninsulated or leaking air, it is time to repair these problems.

Ducts that run through unconditioned spaces, like crawlspaces or basements, should be insulated. If you are unsure of whether or not to insulate, simply place your hand on the duct material. If it feels warm (or cool if distributing cool air), you need insulation. Insulate your ducts to R-6.

If you are insulating heating ducts in an unconditioned space, insulate any water pipes as well. If there are uninsulated ducts and pipes in the same area, the heat escaping from the ducts may be helping to keep the pipes from freezing. For this reason, the water pipes could freeze and burst if they remain uninsulated. Cooling ducts will also require a well sealed vapor barrier on the outside of the insulation to prevent moisture buildup.

You may need to call in a qualified professional to perform these improvements as this is a large job.

 HVAC Main
 Cooling System Selection
 Heating System Selection
 Programmable Thermostats
 Caulking and Weatherstripping
 Insulation Basics

Content updated May 28, 2009

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