Leaks in the air conditioning duct system are one of the top three energy wasters in most homes.

The U.S. Department of Energy did a study a few years ago and found that duct systems leak about 40% of the air they’re moving. In far more homes than you might suspect, the main culprit is a disconnected duct but a typical ductwork design has many other leaks, too.

Where do the ducts leak?

In addition to how much air is leaking from the ducts you need to know where the leaks are. Leakage inside the building enclosure isn’t so bad, because it’s still in the conditioned space. You still don’t want leakage because it causes comfort problems and possible extra energy use. Leakage outside the living space or attic, crawl space, basement, or garage is what you really pay for and sometimes you pay twice.

Whether the ducts leak inside or outside the building enclosure is only one leakage location that matters. Your home is also affected by how much leakage occurs on the return side and the supply side of the duct system. In the graph below marked A, all of the leakage is on the return side of the duct system, the side that pulls air back to the air conditioner. Likewise, the duct leakage could be all on the supply side, the ducts that send conditioned air back into the house. Graph B shows that scenario.

Are you unbalanced?

Let’s put some numbers on it and take a look. First, let’s assume we have a 2.5 ton air conditioner and it’s moving 1000 cubic feet per minute (cfm) of air. On the supply side, the ducts are putting 1000 cfm of air back into the house, because there’s no leakage. On the return side, we have 100 cfm of leakage. That means in this case, the return air ducts are pulling in 100 cfm of air from the unconditioned attic. This unconditioned air is more expensive to cool when compared to air that should be coming from the living space. This will drive up your electricity bill.

Now let’s look at the supply ducts.

Assuming 200 cfm of supply duct leakage, we end up with a negative pressure in the house and more infiltration of unconditioned air.

The two scenarios described above have either all return duct leakage or all supply duct leakage, but all that really matters is that you have unbalanced duct leakage. You most likely will have air leakage on each side.

Finding the professional

Talk to a qualified Design Consultant for your personal comfort and peace of mind. An E.D.S Air Conditioning representative can uncover the truth with regard to your duct system design and its functionality. Accurate air flow and proper balance will prevent high energy costs related to poor duct design or leakage which may be a result of old or damaged ac duct work concealed in your home.