You can wear the warmest, puffiest jacket—but if you leave the zipper undone, you’ll still get cold. Homes work the same way. You might have the best, most efficient heating system money can buy, but if your house has gaps and cracks that let air leak in and out, you’ll never feel truly comfortable. 

Air sealing is one of the most cost-effective upgrades you can make to reduce heat loss and improve comfort—especially in homes that haven’t updated their insulation. 

How do I know if my home needs air sealing? 

Most homes, especially older ones, have small (and sometimes not-so-small!) openings in the building envelope (that’s the roof, walls, windows, doors, and foundation that separate indoors from out).  

Sometimes the signs are obvious, like a draft you feel every time you walk by a window or door. But to get a complete picture, Retrofit Advisors use a tested called the blower door test. To run the test, the Retrofit Advisor temporarily sets up a powerful fan in your front door to pull air out of your house and lower the pressure inside. That causes outside air to rush in through any gaps or cracks—showing exactly where the leaks are. 

Air leakage is often measured in air changes per hour (ACH), but there’s a simpler way to think about it: if you added up all the gaps in your home, how big of a hole would that be? That number is called the equivalent leakage area. 

Here’s an example: one of our volunteers lives in a 1910 semi-detached home in central Toronto. Their blower door test revealed a total leakage area of 495 square inches. That’s like having a nearly two-foot by two-foot hole in the wall—all year round! In their case, air leakage accounted for half of the home’s annual heat loss, but they would have never know this without doing a blower door test. 

How is air sealing done? 

There are two main techniques used to reduce air leakage: 

• Caulking is used around areas that don’t move, like the edges of window and door frames. 

• Weatherstripping is used on things that do move, like doors and operable windows. 

  
  

Other leak-prone areas include spots where plumbing, wiring, or ductwork pass through walls and ceilings—often hidden behind cabinets or in the corners of basements and attics. 

Is it expensive? 

Surprisingly, no. Air sealing is usually under $1,000 and often even less. Compared to many other home upgrades, it’s one of the most affordable ways to make your home feel more comfortable and perform better year-round. Better still, Ontario’s Home Renovation Saving Program has rebates for air sealing (as long as you get an Energy Audit —which includes a blower door test — done first!).  

Can I do it myself? 

Absolutely. Here are some easy, low-cost steps you can take right away: 

• Add or replace weather stripping around windows and doors. 

• Install door sweeps to seal gaps under exterior doors. 

• Keep your fireplace flue closed when not in use. 

  
  

If up for a simple DIY home improvement project, try: 

• Installing foam gaskets behind outlet and switch plates on exterior walls. 

• Using spray foam sealant for larger gaps around windows, baseboards, and wall penetrations. 

  
  

If you’re ready to take on a weekend project, we have an in-depth guide to DIY Air Sealing—non-handy homeowners welcome! 

Is air sealing enough on its own? 

Air sealing is a great first step, but it doesn’t replace the need for insulation or other upgrades like replacing leaky windows. Think of it as laying the groundwork: by stopping uncontrolled airflow, you make your insulation and heating system more effective. 

If you’re thinking about installing a heat pump, starting with air sealing is a smart, cost-effective move that will set you up for success.