We’ve recently written about how the fall is an excellent time to schedule duct sealing for your home. In that post we emphasized how you can save money this way, eliminating up to 30% of the air that goes to waste through air leaks in the ventilation system. Scheduling duct testing is the best way to find out if you need to have leaks sealed up to improve your home’s energy performance.
But there’s another important reason to have your air ducts made airtight, and that’s to protect your indoor air quality. Those air leaks can lead to unhealthy air getting into your living space.
Leaks in the return air ducts
The first place where leaking ducts can create IAQ trouble is in the return ducts, which draw the air from inside the home and bring it to the AC and heater. These ducts run through closed-off areas of a building such as the crawlspace, attic, and between the walls, and they draw air in through any gaps. The air they pull in from these spaces is often filled with air pollutants. The HVAC system filter isn’t sufficient guard against this—it isn’t designed for air quality defense—and leaky air handlers can allow in plenty of these contaminants into your home.
Leaks in the supply air ducts
Air is pushed out the supply air ducts, so there isn’t the same risk of them drawing in contaminants through leaks. The problem here is that as the air escapes through the leaks, it creates negative pressure inside the house.
Think of it this way: if the return vents draw in 10 units of air from the living space of a house, but the supply vents only replace 7 units, losing the rest to leaks, the living spaces end up with a deficit of 3 units of air. Extra air must replace that vacuum—and this air will get drawn from crawlspaces, the attic, or the garage. This isn’t the air you want to be breathing while you’re spending time in your house!