Short answer
Air sealing your home is usually the cheapest way to cut heating costs in Canada, because warm air escaping through gaps can account for a large share of winter heat loss. Start in the attic and basement, where the biggest leaks hide, and get a blower door test if you want to measure the result.
Key takeaways
- Air leaks often account for a large share of a home's heat loss, especially in older houses.
- The biggest leaks are usually in the attic floor and the basement rim joist, not around windows.
- ACH50 measures airtightness; lower numbers mean a tighter home.
- DIY caulk, foam and weatherstripping cost little and handle many leaks.
- Seal before you insulate, and before you size a new heat pump or furnace.
Air sealing your home is usually the cheapest heat you can buy in Canada. Every gap that lets warm air escape pulls cold air in somewhere else. Your heating system has to warm that cold air from scratch, all winter long. In many older homes, air leakage is one of the largest sources of heat loss, often bigger than the walls themselves.
Sealing those gaps typically costs far less than new windows, a new furnace or a heat pump. It also makes every later upgrade work better. That is why energy advisors almost always say to seal first.
Why air sealing your home comes first
Warm air rises. In winter, it pushes out through gaps near the top of your house, mostly in the attic floor. That pulls cold outdoor air in through gaps near the bottom, mostly in the basement. This is called the stack effect, and it gets stronger as the outdoor temperature drops.
Sealing has three benefits beyond lower bills:
- Comfort. Fewer drafts and fewer cold floors.
- Better insulation performance. Air moving through insulation carries heat with it. Fibreglass in particular works poorly when air flows through it. Seal the attic floor before you add insulation. See attic insulation R-values.
- Smaller equipment. A tighter home needs less heating capacity. Seal before a contractor sizes a heat pump or furnace so you do not pay for more than you need.
Where the leaks are
Most people blame windows and doors. Those leak, but the biggest holes are usually hidden.
| Location | Typical leak size | DIY friendly? |
|---|---|---|
| Attic hatch or pull-down stairs | Large | Yes, weatherstrip and insulate the hatch |
| Top plates, wiring and plumbing holes in the attic floor | Large in total | Possible, but attic work is hard and hot or cold |
| Pot lights in the top-floor ceiling | Medium to large | Only with airtight-rated covers or fixtures |
| Basement rim joist | Large | Yes, with caulk or spray foam |
| Plumbing, vent and cable penetrations | Small to medium | Yes |
| Exterior doors | Medium | Yes, weatherstripping and door sweeps |
| Windows | Small to medium | Yes, caulk trim and interior gaps |
| Electrical outlets on exterior walls | Small | Yes, foam gaskets |
| Fireplace damper | Medium to large | Yes, close it or add a chimney balloon |
Understanding ACH50
Airtightness is measured with a blower door test. A fan in an exterior door pulls air out of the house until the pressure inside is 50 pascals lower than outside. The test measures how much air leaks in to replace it. The result is reported as air changes per hour at 50 pascals, or ACH50.
- Older, drafty Canadian homes often test somewhere around 7 to 15 ACH50 or higher.
- Many existing homes from recent decades fall in the 3 to 7 range.
- New homes built to current codes are often tighter still, with targets that vary by province.
- R-2000 homes target about 1.5 ACH50, and Passive House targets 0.6.
A lower number means a tighter home. A blower door test is part of every EnerGuide home evaluation, and many advisors will run the fan while you walk around and feel for leaks.
DIY vs pro air sealing
What you can do yourself
A tube of caulk, a few cans of low-expansion spray foam, foam outlet gaskets, weatherstripping and door sweeps typically cost $100 to $300 for a whole house. Focus on the basement rim joist, plumbing penetrations, exterior doors and the attic hatch. These are safe, quick wins.
When to call a pro
Sealing the attic floor properly means moving insulation, working around wiring and finding top-plate gaps in the dark. Professional air sealing typically costs around $1,000 to $3,000 depending on house size and access. A pro also knows which gaps must stay open, such as clearances around chimneys and flues. Call one if:
- Your attic has vermiculite insulation. It may contain asbestos and should be tested before anyone disturbs it.
- You have older knob-and-tube wiring.
- You have pot lights that are not rated for insulation contact.
- You want a before-and-after blower door test to confirm results.
Ventilation and safety
A tighter home holds more moisture and indoor pollutants. Very tight homes usually need mechanical ventilation, such as a heat recovery ventilator (HRV) or energy recovery ventilator (ERV). Bathroom and kitchen fans should vent outside and actually get used. If you have a fuel-burning furnace, boiler or water heater that draws air from the room, ask a technician to check for backdrafting after major sealing. Always keep working CO alarms.
What it saves
Savings depend on how leaky your home starts. A drafty older house can see a meaningful drop in heating costs. A newer, already tight home will see less. Use the home energy estimator to see how much of your bill goes to heating, then check rebates in your province. Some programs fund air sealing alongside insulation when an assessment is done first.
Frequently asked questions
How much does air sealing cost in Canada?
DIY materials for a whole house typically cost $100 to $300. Professional air sealing usually runs around $1,000 to $3,000 depending on the size of the home and attic access.
What is a good ACH50 for an existing house?
Many existing homes test between 3 and 7 ACH50, and older drafty homes are often higher. Getting an older home below about 5 is usually a solid improvement.
Should I air seal or insulate my attic first?
Seal first. Air moving through insulation carries heat with it, and it is much easier to seal the attic floor before more insulation is added on top.
Can a house be too airtight?
A house cannot be too tight if it is properly ventilated. Very tight homes need mechanical ventilation such as an HRV or ERV to control moisture and indoor air quality.
Want numbers for your own home?
Use the household energy estimator with your province's prices and climate. It takes about two minutes.