Wildfires in Canada are once again sparking air quality alerts up and down the eastern seaboard, as well as the Midwest, just as a heat wave continues to grip the region. Smoke from wildfires is known to contain toxins and other byproducts that can make most anyone feel sick, but especially those with preexisting respiratory conditions and other health issues.

That has a lot of people asking if it’s safe to run their ACs when the air quality is so bad.

Is it safe to use air conditioning when air quality is poor?

Air conditioning systems can prove useful in keeping you comfortable while your home's windows and doors are firmly sealed off from pollution outside. Our home engineering professionals in the Good Housekeeping Institute Home Improvement & Outdoor Lab have long established that most well-made air conditioning units can help maintain healthy indoor air quality.

That said, ensuring your air conditioner's filter is clean and up to date is important when you use AC during any poor air quality events in your area.

If you have central air conditioning units, running your AC system when there's wildfire smoke or other widespread air pollution outside won't put you at greater risk for breathing issues.

"Central air conditioning systems treat virtually all the air in the house as it circulates through the system," explains Dan DiClerico, Home Improvement & Outdoor Director in the Good Housekeeping Institute.

Ronald Grifka, M.D., president of University of Michigan Health-West, says that an effective air conditioning filter could potentially process more air in your home in a shorter amount of time compared to room air purifiers — upward of 100 cubic feet per minute, though both solutions should be used for best results, Dr. Grifka adds.

"So you can really just clean and purify more air with an air conditioning system than a single, small, corner air purifier; from that perspective, air conditioning may be helpful," he says. "The average house built with proper air conditioning systems keeps too much air from the outside getting in; and any air that does creep in, a good filter can be quite helpful to keep the air inside the house as clean and safe as possible."

As for window AC units, there's a common misconception that they continuously pull outside air into your home. In reality, window air conditioners primarily recirculate the air that's already inside your room. While they do use outdoor air to cool the condenser, that air is kept separate from the indoor airflow. If your unit has a fresh-air vent or outdoor air damper (often a small slide lever), make sure it's closed during smoky conditions. The U.S. Environmental Protection Agency (EPA) also recommends checking that the unit is tightly sealed around the window to prevent smoke from leaking indoors.

For better protection, pair them with a portable HEPA air purifier and keep windows and doors closed.

How to keep indoor air safe while air quality is poor

Here are some ways to improve indoor air quality alongside air conditioning, according to our Good Housekeeping Institute experts and leading organizations like the American Lung Association:

  • Close all windows and doors. Consider sealing gaps around doors and windows with weatherstripping, weather-sealing tape, or silicone caulk.
  • Consider replacing AC filters that may be impacted by excessive wildfire smoke or other local air pollution events.
  • If your central HVAC system has a fresh-air intake or ventilation setting, close it (if possible) and set the system to recirculate indoor air.
  • Use a portable air purifier or high-efficiency filter to target fine particles.
  • Avoid activities like smoking, burning candles, and using a gas stove.
  • Pause on vacuuming, as Dr. Grifka says it can stir up dust that is already inside your home.