Leaking Ducts: One Big Problem

Most people don't know it yet, and many actually take it for granted, but the most effective tactic to make their home more comfortable lies just above their heads.

When checking out a home, we ask about the location of the house, the type of the house they're living in, and many more questions we consider basic. The two most important questions however are, "How old is the house?" and "Where are the air conditioning ducts?"

Never take ducts for granted

Experience has taught me that there is always something wrong with 25-year old homes that have ductwork in the attic. In my many years in the industry, most people with comfort issues always have this problem: leaky ductwork.

We measure leakages in ducts in percentage, which means that if your ducts leak 20%, an estimated 20% of the HOT or COLD air pumped into your home is leaking out of the ducts and into the attic. Leaking ducts may also mean that you're system is SUCKING hot or cold attic air back to the house.

Professional energy auditors always target for less than 2-5% duct leakage in new High-Performance homes. Older homes, however, especially those with metal ductwork, usually have a duct leakage of OVER 40%.

Metal Ducts: Old and Without Seals

Way back between 1950 and 1980, people were taking energy efficiency for granted, because energy was INEXPENSIVE. Installers didn't make an extra effort to seal the metal ducts they were working on.

Sections of metal ducts were just slid into each other, and were set into place with a few screws. The ducts were then wrapped with insulation to prevent sweating and condensation, but not to insulate them and make them energy efficient.

If the ductwork is not sealed it leaks. Not sealing ductwork would be like putting copper pipes together for plumbing without SOLDERING the joints.

Imagine an air conditioning duct as a long, hole-ridden garden hose. The pressurized water (or air in an air conditioning duct) will leak out of all the holes BEFORE it gets to the end of the hose. You get a very, very small amount of water out of the hose's end since much of the water has already leaked out. That's what happens with air conditioning ducts that have more than 40% leakage -- most of the HOT or COLD air has escaped out of the ductwork and into the attic, where it's not supposed to be.

Older metal ducts are very prone to leakage. Many studies have proven that there's a direct link between the duct system's age and duct leakage percentage. Also, a duct wrapped with insulation is akin to wrapping a leaking pipe with a rag to stop the leak. The insulation does virtually NOTHING to lessen duct leakage since the air is under pressure.

Leaking air conditioning -- Not good!

Nobody wants higher energy bills, but leaky ducts create negative pressure, increasing energy costs. If there were 20% leakage, the same amount of air would need to enter the house through whatever means, be it through the windows, the doors, can lights, and any other "holes" in the house. Outside air is always dirty, with dust, pollen, and humidity -- this air will enter a home with leaky ducts. You'll know that outside air gets into the home when there's dust on windowsills and carpet stains around baseboards.

A few air-conditioning companies cash in on leaky ducts by offering a new air conditioning unit for thousands of dollars instead of sealing or replacing leaky ductwork. The latter costs only a fraction of the price of a new air conditioner.

Fix the leak!

Basically, there are three methods to fix leaky ductwork. The first method entails stripping off the existing insulation, sealing all seams, and then wrapping the duct with green energy barrier covered duct blanket. The second method is not generally recommended, since it can become expensive. You'll need to tear out the metal ductwork and replace the whole system with flex ductwork.

For the third method, you'll need to contact a spray foam company. The duct insulation needs to be stripped off and the spray foam company will spray about 1-2 inches of closed cell foam on the ducts. This is more efficient, since the foam will seal, and at the same time, insulate the ducts. Some cities, though, do not allow this method, so you'll have to consult your local building codes and even your fire officials.

Remember: don’t take for granted what lies just above your head. Check to see if your ductwork is sealed tight and insulated. An air conditioning system working in tip-top efficiency makes for lower energy bills and a comfortable home.

Photo by Sybren A. Stüvel and Valerie Everett

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Comments 7 comments

whitton profile image

whitton 5 years ago

Very useful information. Here are some ways to determine if you have leaking ductwork.

• Rooms that are difficult to heat or cool.

• Filters that get dirty quickly, indicating leaks in return ducts.

• Streaks of dust at duct connections or register vents

• Poor air flow at registers.


Better Yourself profile image

Better Yourself 5 years ago from North Carolina Author

Thanks for your comments Whitton. You are spot on!


Angela Brummer profile image

Angela Brummer 4 years ago from Lincoln, Nebraska

Another great hub!


Better Yourself profile image

Better Yourself 4 years ago from North Carolina Author

Thanks Angela for taking the time to read my hubs! Hopefully you don't need this info to come in handy any time soon for yourself but it's here to help if needed :)


Linda 3 years ago

Hello ,If it is loose fill insulation like fiasgrlbes or cellulose then the problem might be in the attic. Walk carefully up there or you will fall into the room under you. If its not there then the location could also be a short distance from the place where insulation is building up , with it being just pipe insulation torn up by the intruder.There must be a wharf rat , roof rat , or squirrel tearing holes for bedding or something like that, in there; so carry a stick or a 22 cal. pistol with rat shot . Perhaps, you can mend the pipe with duct tape and a plastic bag and then wrap with some additional fiasgrlbes insulation and tape again.Be sure and seal the entrance that the varmint came through, too. They will most likely try to come back, if they have babies this time of year its an almost certainty , there are babies. Moth granules work but not moth balls to repel male squirrels and females not on the nest. Pantyhose work great to put some into tie off and hang about in the crawl space or attic. You can remove them if kept in pantyhose dispensers later when warmer weather brings the smell inside and creatures back outside.Wharf rats will be in holes in the ground , pack steel wool and rat poison in there to stop them. Watch out for dog and cats poisons will kill 3 times when eaten by the next animals.I have done this many times , just keep searching until you find where the entrance is at and enemy combatants to fight for your air supply.Best Regards, Joe Woodall, Managing Partner Georgia Adobe Rammed Earth Renewable Energy Dewy Rose GA


Wendy 3 years ago

Solar panels are a great idea and I wish I had the skllis to build my own from plans. Maybe I can talk my brother, who is the handy one, into building these. Thank you for the project and information.


Stefany 3 years ago

You're welcome, Eric. Yes, I would think that Omaha is more than a liltte bit colder The only downside to our insulation project was that we were really constrained by our 6'3 ceilings. There were several areas where I had to make tradeoffs between insulation R-value and airflow behind the insulation. In the sloped sections, we are only R-9 due to the 2 4 joists. In the flat ceilings, I was able to get R-26 in most spots. Had we had more height, I would have loved to drop the sloped ceilings just a bit to have more insulation depth.However, with every section of wall and ceiling now having at least some insulation and with a consistent vapor barrier (poly sheet between the insulation and the drywall), the space feels great. There are no drafts or cold pockets. I think we could almost heat each room with a candle. I wish the rest of our house was that comfortable!

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