Wildfire Smoke in Your Home: What to Do Before, During & After

Smoke is outside: do this first

• Check your current AQHI, air-quality alerts and local forecast. In Quebec, use InfoSmog.
• Keep windows and doors closed as much as practical while outdoor smoke is worse, but do not let the home become dangerously hot.
• Run filtration you know is appropriate for the equipment: a properly sized portable air cleaner and/or the highest-quality ventilation filter your system can handle.
• Reduce indoor particle sources such as smoking, vaping, candles, incense and smoky cooking. Limit unnecessary exhaust-fan use.
• Use one cleaner-air room if you cannot keep the whole home reasonably clean and cool.
• If you cannot maintain cleaner air or a safe indoor temperature, use a local cleaner-air or cooling space.

Wildfire smoke is a recurring household problem across Canada, not just for homes beside an active fire. Fine particles can travel long distances, enter through doors, windows, vents and other openings, and remain indoors after outdoor conditions improve. Health Canada identifies PM2.5 as the main health risk from wildfire smoke and notes that air quality can be poor even when you cannot see or smell smoke.

The practical home strategy is simple even when the equipment details are not: reduce unnecessary smoke entry, filter the air that gets inside, avoid creating more indoor pollution, and keep the home safely cool.

Check the AQHI, alerts and smoke forecast

Canada’s Air Quality Health Index (AQHI) runs from 1 to 10+:

The AQHI is not the same thing as the U.S. AQI. Canada’s AQHI is a health-risk index on a 1–10+ scale. The U.S. AQI is a different 0–500 system. Check which scale an app or monitor is showing before interpreting the number.

During wildfire smoke, Environment and Climate Change Canada changes the AQHI calculation when PM2.5 becomes the dominant risk: the AQHI can be calculated hourly using PM2.5 alone so it responds more quickly during high and very-high smoke conditions. An AQHI of 10+ is not a ceiling on pollution; air pollution and health risk can continue to increase after the display reaches 10+.

Useful official tools:

• Current AQHI and AQHI forecasts
• How the AQHI works during wildfire smoke
• WeatherCAN custom AQHI notifications
• InfoSmog for Quebec
• ECCC Air Quality Model Forecast Maps / FireWork

ECCC’s smoke maps are generated twice daily and show hourly wildfire-smoke and PM2.5 forecasts for the next 72 hours. Use them to see the direction of the problem, not as a promise about what your street will look like at 3:17 p.m. Current AQHI observations and alerts matter more for immediate decisions.

Before smoke arrives

Health Canada’s current preparation advice emphasizes readiness rather than trying to turn a normal house into a bunker.

• Know where to check conditions. Set up WeatherCAN AQHI notifications and know your local health authority’s guidance.
• Check filters before smoke season. Clean or replace ventilation-system filters according to the manufacturer and keep replacements on hand.
• Use the best filter your system can safely handle. Do not assume every furnace should get the same MERV rating.
• Have a properly sized portable air cleaner if your plan relies on one. Smoke CADR and room size matter more than app features.
• Pick a cleaner-air room in advance. A bedroom or other room where people spend a lot of time is usually the practical choice.
• Fix obvious leakage. Repair worn weather stripping and poorly closing windows or doors, but do not block required combustion air, flues or safety ventilation.
• Check smoke and carbon-monoxide alarms. Keep them working and follow current certification and placement guidance.
• Keep necessary medications available. People with health conditions should follow their health-care provider’s plan rather than improvising during a smoke event.
• Have a respirator option for unavoidable outdoor time. Health Canada recommends a well-fitting NIOSH-certified N95 or equivalent respirator such as KN95 or KF94 when you must spend time outside in smoke.

See Health Canada’s current preparation guidance.

Smoke is getting into the house

Closing the windows helps, but a closed house still exchanges air with outdoors. Smoke can enter through gaps around windows and doors, vents, air intakes, service penetrations and other parts of the building envelope. Wind and pressure differences keep moving air through those paths.

Exhaust equipment can also matter. A bathroom fan, kitchen hood or clothes dryer pushes indoor air outside. Replacement air has to come from somewhere, and during a smoke event some of it may arrive through leaks in the building envelope. Health Canada therefore recommends limiting exhaust-fan use when it is not needed, while still using kitchen ventilation when cooking requires it.

The house strategy

Reduce what gets in. Filter what gets in anyway. Keep the house safely cool.

1. Outdoor smoke

• AQHI and air-quality alerts
• FireWork smoke forecast
• Changing wind and smoke conditions

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2. Entry paths

• Windows, doors and envelope leaks
• Outdoor-air and ventilation intakes
• Negative pressure from exhaust equipment

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3. Indoor controls

• System-compatible HVAC filtration
• Properly sized portable air cleaners
• A cooler, cleaner occupied room when needed

A normal house is not smokeproof. The practical goal is lower exposure without creating a new problem by overheating the home or interfering with required ventilation or combustion safety.

Close and latch windows and doors

When outdoor air is smoky, keep exterior windows and doors closed as much as practical. Latching a window can improve its seal. Weather stripping can reduce obvious leakage, especially around older operable windows and exterior doors.

But do not seal combustion-air openings, flues, vents or required mechanical ventilation just because smoke is outside. A home is a system. Solving smoke infiltration by creating a carbon-monoxide or moisture problem would be a spectacularly bad trade.

Reduce the pollution you make indoors

When the house is closed up, indoor sources matter more. Health Canada specifically calls out smoking, candles, incense, wood stoves, vacuuming without a HEPA filter and high-VOC cleaning products as sources to reduce during smoke events.

Practical routine:

• do not smoke or vape indoors
• skip candles and incense
• avoid unnecessarily smoky cooking such as heavy frying or broiling
• use the kitchen exhaust when it is needed for safe cooking, especially with combustion appliances
• wet-mop or damp-wipe instead of dry sweeping
• use a HEPA-equipped vacuum if you need to vacuum during the event
• keep wood-burning fireplaces and decorative fires off

Heat and wildfire smoke

This is the decision people get wrong when they treat “keep the windows closed” like a commandment.

Health Canada’s wildfire-smoke-and-heat guidance says protecting yourself from heat is the priority. If you have air conditioning, use it to keep the home cool while keeping windows and doors closed as much as possible. If you do not have air conditioning and outdoor air becomes cooler than indoor air, opening windows can help cool the home even while smoke is a concern.

Health Canada’s 2026 upper-indoor-temperature guidance recommends 26°C as an upper indoor temperature limit to reduce heat risk, especially for older adults, and identifies temperatures above 31°C as a critical threshold where health impacts rise sharply. Those numbers are risk-management guidance, not a reason to wait until a thermometer crosses an exact line before acting. Symptoms, humidity, duration of exposure and individual vulnerability matter too.

Official references:

• Wildfire smoke with extreme heat
• 2026 upper indoor temperature guidance

HVAC, furnaces, heat pumps and ventilation

Central systems can help, but this is where generic internet advice gets reckless.

What filter should you use?

Health Canada’s current homeowner guidance says to use the highest-quality filter your ventilation system can handle, based on the manufacturer’s recommendations. Its cleaner-air-space guidance discusses MERV 13 or higher for systems that can handle the pressure drop, but that does not make MERV 13 a universal drop-in upgrade for every residential furnace.

A more restrictive filter can reduce airflow in some systems. Filter size, surface area, blower capability, duct resistance and how dirty the filter becomes all matter. If your manual does not clearly support the filter you want to use, ask an HVAC professional.

For the detailed version, see MERV 13 furnace filters for wildfire smoke.

Should I run the furnace fan continuously?

Sometimes, not automatically. Filtration only happens while air moves through a useful filter, so longer circulation can increase the amount of air filtered. But whether “fan ON” is the right setting depends on your system, filter, controls, energy use and whether the equipment also introduces outdoor air.

Do not copy a universal thermostat setting from a random checklist. Confirm how your system actually works. The safe general principle is recirculate and filter indoor air when outdoor air is poor, using settings and filters your equipment supports.

What about an HRV or ERV?

Do not use a universal “always turn it off” rule. Health Canada’s cleaner-air-space guidance supports recirculating air when outdoor conditions are poor and drawing in fresh air when the smoke plume abates, but residential HRVs and ERVs vary widely.

Some systems have recirculation modes. Some do not. Some have dedicated outdoor-air filtration. Some homes depend heavily on mechanical ventilation for moisture and indoor-pollutant control. Check the unit’s manual or ask the installer/HVAC contractor how to reduce smoky outdoor-air intake without defeating required ventilation or combustion safety.

Does air conditioning remove wildfire smoke?

Do not assume it does. Air conditioning’s biggest smoke-season benefit may simply be that it keeps the house cool without opening windows. Particle removal depends on the filter and airflow path in the specific system. Central forced-air equipment may filter recirculated air through the furnace/air-handler filter; many room AC and ductless heat-pump systems are designed primarily for cooling and should not be treated as replacements for a smoke-rated portable air cleaner.

Portable air cleaners: enough detail to make the decision

For wildfire smoke, use smoke CADR rather than a heroic marketing claim about how many square feet a purifier “covers.”

Health Canada’s general sizing rule is straightforward: for an 8-foot ceiling, choose a portable air cleaner with a tobacco-smoke CADR at least two-thirds of the room’s floor area in square feet. A 150 sq. ft. bedroom therefore needs a baseline smoke CADR of about 100. Higher ceilings need more capacity.

Use the air purifier size calculator if you want the room-size math done for you.

For actual operation:

• choose a certified unit sized for the room where you will use it
• HEPA or other high-efficiency particle filtration is the priority for PM2.5
• keep the intake and outlet unobstructed
• higher fan speeds and longer run times filter more air
• clean or replace filters according to the manufacturer, and check them more often during heavy smoke
• avoid devices that intentionally produce ozone

Activated carbon is a separate job. It can help with some gases and smoke odours, but there is no widely used performance rating comparable to CADR for gas removal. Carbon does not replace the particle filtration you need for PM2.5.

Need help choosing equipment? Use the air purifier buying guide or the HEPA vs carbon comparison. Commercial product intent stays on the best air purifier Canada page, not here.

One cleaner-air room can be more realistic than the whole house

If whole-home conditions are difficult to control, concentrate your best filtration in the room where people spend the most time, often a bedroom.

A practical cleaner-air room has:

• windows and exterior doors kept closed while outdoor smoke is worse
• fewer obvious air leaks
• a properly sized portable air cleaner
• as few indoor particle sources as possible
• a comfortable, safe temperature
• limited unnecessary traffic in and out

The cleaner-air-room strategy is about reducing exposure, not creating an airtight sealed room. If that room becomes too hot, the heat problem still wins.

See the clean-air room setup guide for the detailed checklist.

Should you measure indoor PM2.5?

A consumer PM2.5 monitor can be useful because it answers a practical question: are the things you are doing making the indoor air better?

Useful comparisons include:

• before and after turning on filtration
• cleaner-air room versus another part of the home
• indoor trend versus outdoor conditions
• what happens after cooking or other particle-generating activities

Do not turn a consumer sensor into a medical-risk calculator. Health Canada does not give homeowners a wildfire-specific indoor PM2.5 number that means “medically safe,” and the outdoor AQHI is not something you calculate from a consumer indoor monitor. Low-cost optical sensors also have measurement limitations, so trends are usually more useful than worshipping every decimal.

If you are buying a monitor, see the indoor air quality monitor guide.

If smoke is severe or lasts for days

When smoke persists, the goal is sustainable exposure reduction rather than an exhausting ritual of checking the sky every five minutes.

• concentrate filtration where people sleep and spend the most time
• keep checking current AQHI, alerts and heat conditions because they can change quickly
• keep filters from becoming badly loaded
• minimize unnecessary time outdoors
• use a cleaner-air public space if you cannot maintain acceptable conditions at home
• follow current public-health guidance more carefully for household members who are more likely to be affected by smoke

Health Canada identifies groups more likely to experience health effects, including children, people over 65, pregnant people, people with lung or heart conditions, people who work or exercise outdoors, and people facing social or housing conditions that make exposure harder to avoid. This page is home guidance, not individualized medical advice.

If you have to go outside

A well-fitting, properly worn NIOSH-certified N95 or equivalent respirator such as a KN95 or KF94 can reduce exposure to fine particles. It does not protect against gases in wildfire smoke. Facial hair can reduce the seal. Public Health Agency of Canada guidance also says respirators should not be used by children under 2, anyone who has trouble breathing while wearing one, or anyone who needs help removing it.

Read the federal respirator guidance for wildfire smoke for fit and safety details.

DIY filtration is a backup option, not fake magic

Health Canada and BCCDC both provide safety guidance for DIY box-fan air cleaners. They can be useful when commercial air cleaners are unavailable or unaffordable, but they come with more operational caveats.

The big safety rules are simple:

• use a clean, newer 2012-or-later certified box fan with a safety fuse
• use an appropriate high-efficiency filter; BCCDC recommends MERV 13 where practical
• keep the fan away from walls, furniture and curtains
• replace dirty filters so the fan does not overheat
• never leave it unattended while running or while you sleep
• never leave children unattended with it running
• do not use an extension cord for the Health Canada setup

Build instructions belong on the DIY box fan filter guide.

After the smoke clears

Do not use an arbitrary clock time. Check current outdoor conditions first. Health Canada’s July 2026 guidance says that once outdoor air quality improves, you can start replacing polluted indoor air with cleaner outdoor air.

1. Check AQHI, InfoSmog, alerts and weather. Make sure the improvement is real, not just a brief lull you inferred from the smell.
2. Ventilate. Run your ventilation system and open doors/windows to replace indoor air with cleaner outdoor air.
3. Wet-mop hard surfaces. This removes settled dust without kicking as much of it back into the air.
4. HEPA-vacuum carpets and rugs. Avoid a vacuum that simply redistributes fine particles.
5. Clean or replace filters as needed. Check ventilation-system and portable-air-cleaner filters and follow the manufacturer’s instructions.
6. Test smoke and CO alarms. Replace batteries when necessary.

What smoke smell can and cannot tell you

Your nose is not a PM2.5 monitor.

Health Canada explicitly notes that air quality may be poor even when you cannot see or smell smoke. The reverse matters too: noticing an odour tells you smoke-related compounds are present, but smell alone does not tell you the PM2.5 concentration or the AQHI.

Particle filtration and odour control are also different jobs. HEPA/high-efficiency filters target particles. Activated carbon can help with some gases and odours, but performance depends on the media and there is no standard gas-removal rating comparable to smoke CADR.

If lingering odour is your main question, start with HEPA vs carbon filters, then ventilate with cleaner outdoor air when conditions improve and clean settled residue as appropriate.

Common wildfire-smoke mistakes

Canadian context

Okanagan homeowner context: ReadyHome researcher Chris Gaglardi lives on a rural property in British Columbia’s Okanagan, where wildfire smoke and nearby fire-preparedness alerts are recurring household realities. He has not evacuated his current home because of wildfire and is not a public-health, HVAC or wildfire professional. The recommendations here are built from current Canadian primary guidance and clearly scoped homeowner decisions.

The short version

When smoke rolls in, do not chase perfection. Check the AQHI. Reduce unnecessary outdoor-air entry. Filter the air you actually occupy. Avoid making more particles indoors. Keep the home safely cool. Move to a cleaner/cooler space if the house cannot do both jobs. Then ventilate and clean once outdoor air improves.

The specialist guides below take over when you need sizing, equipment selection or detailed setup instructions.