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