Bright Ideas for Saving Energy #2 – Check your Ducts


If you have any ducts in your home for heating or air conditioning, you might be losing a huge amount of energy. The good thing is, many of these problems are very easily solved if you’re not afraid to get a little dirty. How does five minutes and a roll of tape sound for a 30% energy efficiency improvement sound?

Attic Mounted Air Handlers

If the main blower (called an ‘air handler’) of your system is mounted in the attic, there’s a really good chance that you’re losing a significant amount of your system’s efficiency due to air leaks.

The air handler distributes air throughout the house. If you look up in the attic, you’ll see a variety of ducts going to and from the air handler. Every connection is suspect, but the worst problems are usually due to leaks where the air handler sucks air in.  This is called the “return” side of the system because the air is returning back to the system from the house.

Why are return air leaks so bad?

Think about the air in an attic. It’s dusty and usually filled with fiberglass particles. It’s also super hot in the summer and cold in the winter. The humidity in the attic usually matches the outdoor humidity, so that it’s very dry in the winter and damp in the summer. Any time there’s a leak on the return side of the system, that nasty attic air is getting sucked in and distributed around the house. Not only is this a serious efficiency problem, it can have health consequences.

How bad are return air leaks?

Consider a typical winter night when the heating system runs. It might be 30 degrees F in your attic. When the system sucks that air in, it has to raise it up to 100+ degrees to heat your home. This is as compared to heating up the 70 degree air in your house. This temperature difference multiplies how hard the system has to work. It is typical for the system to have to use two to four times as much energy to heat the air from the attic as the air from the house. That means a 10% leak gets multiplied to a 20%-40% decrease in your system’s efficiency!

During the summer, the same thing occurs, except now the system is sucking 130+ degree air in and trying to lower it to 50F for air conditioning. Now things get really bad! Your air conditioner cannot reduce the temperature of the air that much, so the system does a much worse job at air conditioning. Plus, it’s pulling all the humidity in, which makes the system work even harder. The net result is that your air conditioner can be almost worthless, or worse than worthless because it will be pulling in so much hot and humid air.

How do I know I have duct leaks?

There are a few telltale signs of return air leaks:

  • Very dusty house – if you clean often and yet you find the house gets dusty fast, you probably have a serious leak.
  • Very dry air in the winter
  • Very humid air in the summer, in spite of air conditioning
  • You feel drafts from the air registers when the system isn’t running
  • Your air filter gets dirty quickly
  • You can see the leaks

Where do I look for leaks?

The first thing to do is look at your air handler. The most common problem is when there’s no cover over the filter slot. This problem will easily decrease the efficiency of your system by 30%. In addition, you’ll find that the filter clogs up very quickly, like this one that is completely covered in dirt.

The next place to look is around the ducts near the filter. You can use a smoking incense stick and watch the smoke as you move it around the air handler while the system runs. If there’s a leak, the smoke will suck in, leading you right to the source of the leak! You can also purchase a cheap smoke gun, which works like a fog machine.

Another common place for leaks is where the ducts attach to the ceiling. They’ll usually be connected to the ceiling via a sheet metal box called a “duct boot.” Follow the ducts to each boot. Before you touch anything to look at the boot, take a look at the insulation around it. If it looks dirty or discolored, that’s a sure sign of a leak. It might be a duct leak or a leak from the house into the attic. In either case, you want to find the problem and seal it up.

It’s beyond this post to go into all the details about proper duct retrofits, but at least you can find them and know why you need to fix the leaks. One hint though – never use “duct tape” for sealing ducts. It’s not named right. It will always fail.

How do you know if your air handler is leaking into the attic?

Sometimes it’s really obvious. Sights like this may me cringe.

Leaks from the air handler into the attic can be pretty obvious during the winter. If you see a lot of snow melting off your roof, usually there’s a duct leak below it in the attic. So the first thing you should do is look at the outside of your house if there’s snow on the roof. There’s another post all about this that will help you find those problems.

The easiest thing to do is check where all the ducts connect to the air handler and the main trunk line (the big duct that comes off of the air handler, to which all the other ducts are attached). Make sure that all the ducts are tightly attached and air-tight. Each duct that is lose could be responsible for a 5%-10% decrease in your system efficiency.

This should be enough to get you started. For minimal investment in time and supplies, you can often improve your system’s energy efficiency by more than you could by purchasing a new, high-efficiency system. Even if you did buy a new system, if you don’t fix these problems, it will still work more poorly than an average system with excellent ducts.

The general rule is – if it looks wrong, it probably is!

-Happy hunting

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