Fix your Air Duct Leak, Pad your Wallet

My Attic Air Duct

The following article was written by Rod MacKenzie, an energy auditor based in Atlanta. Rod operates Green Building Resources, which is a residential energy auditing firm that provides customers with the products and services they need to make their home more comfortable and more energy efficient - home improvements that pay you back 2 ways!


We’re going to talk about how to detect leaks in the heating, ventilation and air conditioning system (aka the HVAC system).

Leaks in the duct system are quite common and even more invisible than air leaks around windows and doors. Why are they more invisible? Because duct system air leaks are in places you don’t usually go – like the attic or crawlspaces of your home. The most common place for duct system air leaks is near the HVAC unit itself or in the joints of the duct system.

Your HVAC system is working hard to cool air in the summer or heat it in the winter. But if your duct system leaks, you’re probably not getting the full benefit of your HVAC system and you may come to the false conclusion that you need a new system.

Detecting leaks in your HVAC system is possible with a Duct Air Leak Test. The machine used in this test is sometimes called a “Duct Blaster” which sounds ominous - but don’t be concerned – the machine will not harm your duct system. It simply blows air into the duct system and allows a technician to find any and all air leaks so they can be sealed.

The duct blower machine is a small fan attached to a flexible and expandable pipe that resembles a piece of the duct system. The end of the pipe is attached to the duct system by temporarily taping it to one of the HVAC system outlets (one of the grills where conditioned air comes out)

After some other prep work, the machine is turned on and it blows air through the duct system and measures how much air is escaping. If the duct blower machine operator is really fancy, he/she will flow some theatrical fog through the fan so you can actually see where the air leaks are.

Keep in mind that all duct system leaks are NOT the same. Duct leaks in the attic or other unconditioned places are the highest priority because you never get any benefit from those kind of leaks. However, duct system air leaks inside your interior walls or between conditioned floors are not so bad as the leaks will still work to heat or cool the home even if it doesn’t complete it’s trip through the duct system.

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as an A/C contractor....Bwwwwwaaaaaaaaa ha ha ha ha B.S !!!
Today I called our AC Technician to help us find out why our room temperature is in the middle to high 80s when we set the AC on 78 on a typical Kansas summer day. He checked the frion, which was fine and cleaned the AC unit, which he said was filthy. We also wanted him to check some leaks in the air ducts in the crawl space where my husband recently noticed a gush of air streaming out of the main duct under the house. The technician's respond to that was that it is ok for air to leak into the crawl space because it will keep the water pipes from freezing in the winter. What is your opinion on that?
ckmapawatt's picture
Karin, I'm no AC technician or expert in the field, but that sounds like a B.S. response. Your house should be designed so that the pipes shouldnt freeze in the winter. You shouldnt have to rely on an air-leakage for that to happen. What did he have to say about air leakage in the summer? Surely he didnt say, "So it can keep the water cooler." It sounds like you need to get a new AC technician. I would call the company he was with and ask if this is standard practice (to recommend air leakage). My advice: Get the leak fixed ASAP! All your cool air is going into your crawl space!

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