Wildfire Smoke and Your Home: Keeping Indoor Air Cleaner in BC

When wildfire smoke reaches the Lower Mainland, some of it gets indoors. For homeowners and renters, here is where to check the air, how to keep one room cleaner and cool, what to ask in a strata building, who should take extra care and what to look for when you buy a home.

The short version

Where to check the air

The Air Quality Health Index (AQHI) rates the health risk from air pollution on a scale of 1 to 10+, and BC calculates it in a way that better reflects smoke.

• Metro Vancouver. Issues air quality warnings for Metro Vancouver and parts of the Fraser Valley Regional District: yellow for high health risk and orange for very high. Its AirMap shows real-time readings, the AQHI and a two-day forecast, and you can sign up for email alerts.
• The Province. Elsewhere in BC, the Province issues Air Quality Warnings, which used to be called smoky skies bulletins, with alerts by email or text.
• Stick to official sources. The BC Centre for Disease Control (BCCDC) says other sites and apps may not reflect BC's measurements.

BCCDC groups the AQHI as low (1 to 3), moderate (4 to 6), high (7 to 10) and very high (above 10). At moderate, people at higher risk who have symptoms should consider cutting back on strenuous outdoor activity. At high, people at higher risk should cut back whether or not they have symptoms, and at very high, avoid it; everyone else should then cut back too.

Keep smoke out, but stay cool

BC's air quality warnings advise keeping windows and doors closed as much as possible, but BCCDC says overheating poses a bigger health risk than smoke for most people who are at risk. For people susceptible to heat, it treats indoor temperatures of 26°C to 31°C as possibly risky and above 31°C as dangerous.

• Cool and clean together. BCCDC suggests air conditioners, heat pumps, fans and window shades to keep a cleaner-air space comfortably cool; see keeping your home cool in a heat wave.
• If you can't do both. Choose staying cool: stay with family or friends who have air conditioning, or spend time in a community centre or library, which tend to have cooler, cleaner air.
• Cut indoor sources. Interior Health suggests avoiding smoking or vaping indoors, wood stoves and candles, and Health Canada suggests limiting exhaust fans, such as bathroom fans.

Portable air cleaners and box fan filters

A portable air cleaner plugs into an outlet and cleans the air in one room. BCCDC says most use HEPA filters, which trap the very small particles in smoke, and that in most studies they cut small particles by 40% to 80%. Use it in the room you use most, such as a bedroom.

• Size it to the room. Look for an Association of Home Appliance Manufacturers (AHAM) label. Health Canada says its tobacco smoke clean air delivery rate (CADR) should be at least two-thirds of the room's floor area in square feet, assuming an 8-foot ceiling: for example, at least 100 for a 150-square-foot bedroom.
• Run it well. Keep doors and windows closed, run it continuously, and don't block it with walls or furniture.
• Skip ozone. Health Canada advises against devices that produce ozone, and BCCDC says ozone generators and ionizers can't effectively remove smoke particles.

A do-it-yourself box fan filter costs less. BCCDC's design uses a clean 20-inch box fan made in 2012 or later, with a safety fuse and a UL, CSA or Intertek ETL mark, and one or two 20-by-20-inch MERV 13 furnace filters taped to the back, airflow arrows matching. Keep it clear of curtains, change the filter when it looks dirty and never leave it running unattended. Health Canada adds: not while you sleep, and not on an extension cord.

Furnace filters, heat pumps and HRVs

• Furnaces and central systems. Health Canada suggests the highest-rated filter your system can handle, following the manufacturer, and BCCDC's smoke guidance for schools recommends a rating of MERV 13 or higher where the equipment can take it. BCCDC suggests asking your service provider which filters and settings to use on smoky days. Ask about running the fan continuously too; health authority guidance for care facilities keeps air moving through the filters during smoke events.
• Change filters regularly. Health Canada notes that clogged filters aren't effective at removing smoke.
• Heat pumps. A heat pump or air conditioner lets you keep your cleaner-air room cool with the windows shut; see Heat Pumps in BC.
• HRVs and ERVs. Heat and energy recovery ventilators exchange stale indoor air for outdoor air. BC Housing's guide says they're meant to run continuously, that switching one off for long periods lets indoor pollutants and humidity build up, and that the fans in most aren't sized for higher-performing filters. Ask your installer how to run yours on smoky days.

Condos, townhouses and other stratas

Some apartment buildings have shared ventilation, such as a central make-up air unit serving the corridors on every floor. Under the Strata Property Act, the strata corporation must repair and maintain common property. Fraser Health and Vancouver Coastal Health advise owners and managers of rental and strata housing to:

• Plan ahead. Have a smoke readiness plan, maintain the HVAC system and subscribe to air quality alerts.
• Filter better. Reduce outdoor air intake and upgrade filters to the highest rating possible, ideally at least MERV 13, without reducing building pressure.
• Offer a cleaner space. Consider a cleaner air space in a common room, with portable HEPA or do-it-yourself air cleaners.

Ask council or the property manager whether there's a plan, what filters the shared systems use and when they were last changed; renters can ask their landlord.

Who is most at risk, and when to get help

BCCDC lists people at higher risk of severe or long-term effects: people with chronic conditions such as asthma, chronic obstructive pulmonary disease (COPD), heart disease and diabetes, people who are pregnant, infants and small children, and older adults.

• Milder symptoms. HealthLink BC lists eye irritation, runny nose, sore throat, mild cough, phlegm, wheezing or headaches, which can often be managed without medical care. If they don't improve with less exposure, or get worse, get prompt medical attention.
• More serious symptoms. Shortness of breath, a severe cough, chest pain or heart palpitations need prompt attention. If it's hard to breathe in smoky air, get care right away; in an emergency, call 9-1-1.
• Advice and medication. Call 8-1-1 for non-emergency advice. HealthLink BC says people who use rescue medication, such as an inhaler, should carry it at all times during wildfire season.

If you must be outdoors, BCCDC suggests a well-fitted N95, KN95 or KF94 respirator, and less exercise on smoky days.

Buying a home with smoky days in mind

A showing on a clear day won't tell you how a home copes with smoke, so ask:

• Filtration. Does the furnace or air handler take a MERV 13 filter, and when was it last serviced?
• Cooling. Is there a heat pump or air conditioning? If not, could you add one, and would a strata's bylaws allow it?
• Ventilation. For an HRV or ERV, ask for service records. BC Housing's guide suggests cleaning or replacing its filters every three months and an annual service by an accredited contractor.
• Sealing. Health Canada's guidance includes properly sealing windows and doors, so check that they close tightly.

Radon is another indoor air question; see Radon in BC Homes. For protecting the property itself, see Wildfire Risk and Your Home in BC.

Questions homeowners often ask me

Should I keep my windows closed when it's smoky?

As much as you can, but not at the cost of overheating, which HealthLink BC says is usually the bigger risk. If your home gets too warm with the windows shut, cool one room, or spend the hottest hours somewhere cooler, such as a library.

What size air cleaner do I need for a bedroom?

Check the tobacco smoke CADR on the AHAM label. Health Canada says it should be at least two-thirds of the floor area in square feet for an 8-foot ceiling, so a 120-square-foot room needs at least 80. Choose a larger unit for a higher ceiling.

Is a box fan air filter safe to use?

Yes, with care. Use a clean, certified box fan made in 2012 or later with a safety fuse, plug it straight into the wall and change the filter when it looks dirty. Don't leave it running unattended or while you sleep.

Should I turn off my HRV when it's smoky outside?

Check the manual or ask your installer first. BC Housing's guide says these systems are meant to run continuously, and a long shutdown lets pollutants and humidity build up indoors. If you change a setting for smoke, switch it back once the air clears.

Does a HEPA air cleaner remove everything in smoke?

No. HEPA filters remove fine particles, not gases. BCCDC says units with activated carbon filters can also reduce gaseous pollutants, though Health Canada notes there is no widely used rating system for filters that remove gases.

Buying a home? Read what a home inspector checks, or the strata documents to read before you buy.

This article is general information, not medical or professional advice. The details come from the BC Centre for Disease Control, HealthLink BC, Health Canada, the Province of BC, Metro Vancouver, Fraser Health, Vancouver Coastal Health, Interior Health, BC Housing and the Strata Property Act, and were current at the time of writing; follow current air quality warnings and your health care provider's advice. For BCCDC's guidance, see BCCDC's wildfire smoke page.