Duct Sealing and Insulation

Overview

If you could improve the efficiency of your existing furnace or air conditioner by 10 - 30% without the major expense of replacing the heating or cooling system itself, why wouldn't you do it? Welcome to one of the most boring, and yet one of the most cost effective, concepts in home energy efficiency... Sealing and insulating your heating and cooling ducts.

Details

If you've got a forced air heating or air conditioning system, duct sealing and insulation is something that you need to know about if you want to be energy savvy. Most homes with unsealed/insulated ducts lose between 10% - 30% of the energy used for heating and cooling because the nice warm (or cold) air in their air ducts leaks out before it reaches the living space. In other words, almost a third of what you're paying to heat or cool your home is wasted before it ever gets to you.

Here's what you need to know:

Most air leaks in ducts happen at joints and seams in the ductwork, not on the smooth, straight parts of the ducts.
An easy do-it-yourself test to look for obvious air leaks in your ducts is to hold up a candle (or even better, a stick of incense if you can find it) to the junctions and seams of your ducts. If you see the flame (or smoke) getting pulled in or pushed away from the duct, there's some air leakage going on in that spot.
Some of the worst problems with duct leakage occur when the furnace and ductwork is in a basement that doesn't have wall insulation and is very cold. That's because when the duct (with very hot air inside it) is surrounded by very cold air in a cold basement, there's a big opportunity to lose heat.
For air conditioning systems, some of the worst problems occur when your air conditioner is outside of your home, on your roof or in your attic. The exposed ducts there can have the same problem as heating ducts in a cold basement.

The good news is that fixing this problem isn't usually too expensive, and the impact is usually so big that the project often pays for itself with a year or two. If you're going the do-it-yourself route, you can make a difference by getting mastic tape and taping all the seams and junctions of your ducts (including where it connects to your furnace or air conditioner).

Don't forget the return ducts as well — many times, return ducts are built into walls and if they are pulling air from outside the home, your furnace/air conditioner's effectiveness will suffer as well. You've got to be careful to seal every junction and seam where there's leakage — otherwise, the air will just leak out even faster from spots you missed. Add duct insulation, made of foil or vinyl, after the duct sealing is complete.

If you'd like to find a professional who can help do this for you, we can help you find an expert in your area or check out our directory of energy efficiency specialists in your area.

Last Updated: February 2010

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