There’s a lingering belief that a house needs to breathe. That is, it should have some way for air to escape to create better flow and comfort. That’s something of a vestigial organ from days gone by. A well-sealed home is a more efficient home, period. It’s also safer and more comfortable. The process of air-sealing—locating and filling in any gaps in the building to ensure outside air stays outside and inside air stays inside—is one more homeowners should think about.
Consider this: Air leakage, according to Energy Star, eats up between 20% and 40% of the energy spent heating and cooling a typical home. The reason? When outside, unconditioned air enters through, say, a drafty window or a gap in an attic, systems have to work harder to maintain temperature and filter that air. In addition to causing strain on HVAC systems and higher utility bills, any unsealed areas in a house can run uncomfortably hot in the summer and cold in the winter.
The benefits of air sealing
While lower energy bills and general home comfort are two good reasons to air seal a home, the most important is to maintain healthy indoor air quality, says Asa Foss, a building scientist and manager of the Department of Energy’s Residential Buildings Integration program for multifamily and manufactured housing. “Outdoor air is creeping into your home and bringing particulate matter into your house,” he says. A 2024 study published in Environmental Science & Technology found that 75% of the total health impact of all indoor pollutants are from particulate matter.1 “Air-sealing’s job is to keep that outdoor air, oftentimes riddled with particulate matter, outside.”
When all gaps are properly sealed, heating and cooling systems don’t have to work as hard to maintain temperature, lowering their load and your energy bill. The EPA estimates that when a typical U.S. home is air-sealed and properly insulated, homeowners can shave around 15% from their costs.
Additionally, anyone looking to add energy upgrades like a heat pump would be wise to investigate air-sealing first. Otherwise, you may have to spend more on a system that is calibrated to a home where air is escaping. “You might need a 2.5-ton instead of a 3- or 3.5-ton,” he says, referring to the size of heat pumps. “That will save you hundreds if not thousands more on install costs. And it’ll make that heat pump work better, too.”
How air sealing works
Air sealing is the process of identifying and plugging all the spots where leakage occurs. This includes window and door frames, areas where piping enters, crawlspaces, whole-home fan systems, fireplaces, and all other structural elements that serve to separate the outside from the inside. All these create what’s collectively known as the “building envelope.” A well-sealed home is free of drafts and heat pockets, has good airflow throughout, maintains a more consistent temperature, and has less moisture.
The best way to spot where a home is losing its climate-controlled air is to hire a contractor who specializes in insulation to check out your home. This can also be rolled into a broader Home Energy Audit; though that process also includes assessments of appliances, HVAC, and other major home systems. To find those holes, contractors commonly use what’s known as a blower door test to examine building pressurization. They hook a big fan to the front door and blow air out of or into the home. Based on how hard that fan is blowing, the contractor determines how many air leaks are inside a home. “The science is air in equals air out. But the real thing is that they’re able to walk around and pinpoint the actual sources,” says Foss. “They can feel with their hands and use other diagnostic tools to pinpoint the major sources of air leaks.”
When inspecting for leaks, the Department of Energy flags a variety of locations at sites of potential breaches in the building envelope. Outside, these include exterior corners, outdoor water faucets, places where siding and chimneys meet, and areas where the foundation and the bottom of exterior brick or siding meet. Inside leaks can happen in dozens more spots, including electrical outlets, switch plates, door and window frames, electrical and gas service entrances, baseboards, weather stripping around doors, fireplace dampers, attic hatches, wall- or window-mounted air conditioners, cable TV and phone lines, places where dryer vents pass through walls, and vents and fans. If a home’s doors and windows are old, they can also be major leak sources.
Once all the leaks have been identified, contractors get to work sealing. They fill the gaps with caulk, weatherstripping, spray foam, flashing, and other such products.
Can you DIY any of this?
It’s possible to do some air sealing work yourself, but those jobs will mostly be smaller ones. If you feel a draft around certain window and door frames, bust out the caulk and some weather stripping and get to sealing. Caulk is best for cracks and openings between stationary house components like door and window frames, while weatherstripping is used to seal things that move such as doors and operable windows. If you, say, feel air coming in through gaps in pipework in the basement or beneath your sink, it’s fine to grab a can of spray foam and seal it up as well.
While helpful, Foss cautions that these smaller bits of draft sealing aren’t really going to have much of an impact. “Doing those little weatherstripping things is not going to move the needle on the amount of leakage in your home,” he says. “That’s going to be 1 or 2 or 3% of the leaky air. If you feel a breeze, go crazy. Nobody’s going to tell you not to do that. But nothing is going to be impactful, aside from maybe minimizing that one particular breeze.”
The real air-leakage trouble areas are basements and attics, due to the stack effect in which air moves upwards and downwards due to thermal differences. “Because hot air rises, the air leaving your home has to be made up somewhere and it’s usually towards the bottom of your house,” says Foss. “That drives this giant convective loop, where cold air is getting sucked in and hot air is getting pushed out.” In a house that’s not well-sealed, that contributes to most of the air leakage.
While it’s possible to DIY air-seal in basement and attic areas, Foss strongly urges everyone to hire a professional. Air sealing requires a lot of tools and the know-how how to close every single gap. It also requires a lot of building knowledge and time spent in tight, dirty areas like crawlspaces and behind attic walls. Sure, you might be able to seal around the band joist where the foundation meets the floor or close some gaps in the attic. But complete air-sealing, per Foss, is a job that really requires a professional.
How to find a good air-sealing contractor
The ideal company for the job, per Foss, is most likely going to be an accredited insulation contractor. Air sealing and insulating are complementary to a home. Air sealing is essentially wearing a windbreaker, whereas insulation is wearing a wool sweater, Foss explains. “If you’re outside and you’re wearing just a wool sweater, you’re going to get cold because the wind is whipping through you. If you’re just wearing a windbreaker, you’re going to get cold,” he says. “You need a sweater, and you need the windbreaker and when you have both of those, you’re going to stay comfortable in the wintertime. That’s exactly what we’re doing to our houses: We need a sweater and windbreaker.”
The Department of Energy maintains a list of accredited insulating and air-sealing contractors and affiliated institutions. “I’d recommend reaching out to most of them, getting a scope, comparing bids, and then again making sure that air-sealing is part of their work,” Foss says. “If there’s an air-sealing contractor that’s only talking to you about insulation and doesn’t bring up air-sealing, that to me is a red flag, and you should look elsewhere.”
Pricing out the work is a bit difficult, as it depends on such factors as the size of a home, the amount of air leakage, how much insulation needs to be added, and how much demo work needs to be done to get to those leaky spots. However, Foss says to expect estimates in the $1,000 to $5,000 range. For most homes, it should run a couple thousand dollars. Incentives can lessen some of that sting: The Energy Efficiency Home Improvement Credit, which allows up to $3,200 in credit for qualified energy efficiency upgrades, includes a $1,200 max for insulation, air sealing, energy audits, central A/C, and more.
Is it worth the cost? According to Foss, it’s a big yes. “Going from a pretty leaky house to a tighter house is going to reduce your air leakage by 25%,” he says. “Homeowners are going to notice that meaningful change in temperature. They’ll see some significantly improved comfort. That’s worth a big chunk of change, in my opinion.”
- Harm from Residential Indoor Air Contaminants, Environmental Science & Technology, Jan. 2024 ↩︎