Mother and child reading indoors with an air purifier while wildfire smoke hazes the sky

Wildfire Smoke Survival Guide for Canadians

10 min read · Health & Safety

Wildfire smoke now reaches almost every part of Canada each summer, not just BC and Alberta. The biggest health concern is fine particulate matter (PM2.5) – particles small enough to reach deep into the lungs. The good news: the right filtration indoors makes a real difference.

Wildfire burning in a Canadian boreal forest with a large smoke plume
Smoke from boreal forest fires can travel thousands of kilometres and affect air quality across the country.

Know the AQHI

Canada's Air Quality Health Index runs from 1 to 10+. Check it on the Government of Canada weather site or WeatherCAN app.

  • 1–3 Low risk: normal activities.
  • 4–6 Moderate risk: people with heart or lung conditions, children, seniors and pregnant people should reduce strenuous outdoor activity.
  • 7–10 High risk: at-risk groups should avoid strenuous outdoor activity; everyone should consider reducing it.
  • 10+ Very high risk: stay indoors with clean air as much as possible.

Before smoke season

  • Install a MERV 13 furnace filter, and keep two spares – smoke loads filters quickly and stores sell out.
  • Get a portable HEPA air purifier sized for your bedroom or main living area.
  • Check window and door seals and weatherstripping.
  • Know where your HRV/ERV controls are, if you have one.

During a smoke event

  • Close windows and doors.
  • Set your furnace fan to "ON" (not "AUTO") so air passes through the filter continuously.
  • HRV/ERV: reduce or follow the manufacturer's guidance for smoke – many bring in outdoor air.
  • Create a clean-air room: pick a bedroom, close it up and run a HEPA purifier.
  • Avoid adding indoor pollution: no candles, incense, frying or vacuuming without a HEPA vacuum.
  • Check your filter weekly and replace it when it looks dark grey.
  • If you need to go outside, a well-fitted N95 respirator offers far better protection than cloth or surgical masks.

DIY box-fan purifier

No purifier? Tape a MERV 13 filter (20" x 20" works well) to the intake side of a box fan, with the airflow arrow pointing toward the fan. Four filters taped into a cube (a Corsi-Rosenthal box) work even better. Never leave a DIY fan running unattended.

After the smoke clears

  • Replace your furnace filter – it has done heavy work.
  • Air out your home once the AQHI is low.
  • Wipe surfaces and vacuum with a HEPA vacuum to remove settled ash.

Who's most at risk

Children, seniors, pregnant people, outdoor workers and anyone with asthma, COPD, heart disease or diabetes. If you have symptoms like trouble breathing, chest pain or a severe cough, contact a health professional or call 911. Always follow evacuation orders from local authorities.

Be ready before the smoke arrives. Shop MERV 13 filters and HEPA filters, made in Brampton, Ontario. Buildings and facilities can request a bulk quote.

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