As wildfire smoke from Canada and Minnesota creates hazardous air quality across the U.S., experts warn that standard air conditioning systems often fail to filter out fine particulate matter. While closing windows and running purifiers are recommended, air conditioners themselves are rarely designed to clean indoor air of dangerous pollutants.
Why Your Air Conditioner Isn’t an Air Purifier
As smoke from wildfires in Ontario and northern Minnesota blankets a large swath of the U.S., many residents are relying on their air conditioning units for relief. However, HVAC experts and environmental authorities warn that relying on an AC to clear the air is a common mistake.
According to Gothamist, most window air conditioners primarily recirculate indoor air, but many also feature fresh-air vents or outdoor dampers that can inadvertently pull smoky air into your living space. Experts emphasize that an air conditioner’s primary function is temperature control, not air filtration. The AC may keep your apartment or your room cool, but it's not the device that you want to use to try to ensure that you've got good air quality,
noted William Bahnfleth, professor and director of architectural engineering at Penn State University.
Managing HVAC Systems and Window Units
For those using central air, the efficacy of the system depends heavily on maintenance and filter quality. Renters, in particular, face challenges regarding system upkeep. You're kind of at your landlord's mercy in terms of them cleaning their systems,
said Cole Goldklang, founder of Breasy, as reported by Gothamist. Bahnfleth expressed skepticism that most urban central systems are equipped to handle the sudden influx of smoke particles, noting, On short notice and the way this kind of emergency has popped up, I would doubt that most systems are prepared to deal with it.
To minimize risk, the Environmental Protection Agency (EPA) advises residents to keep windows and doors tightly sealed. If you use a window unit, ensure that the outdoor air damper is closed. If the damper cannot be closed, NBC Chicago reports that it is safer to avoid using the unit entirely. For portable units, those with a single hose vented out of a window should be used as little as possible, as they can draw more smoke inside.
The Critical Role of MERV 13 and HEPA Filtration
When upgrading home air quality, the filter rating is the most important factor. The Minimum Efficiency Reporting Value (MERV) scale measures a filter’s ability to capture particulates. According to NPR, a MERV 13 rating is the recommended threshold for effectively removing fine particle pollution, including smoke and bacteria.
For those seeking high-efficiency solutions, HEPA (high-efficiency particulate air) filters are considered a strong option.
“A well-sealed HEPA filter is more than 99.9% efficient for all sizes of particles.”
NPR
Health Risks and Long-Term Indoor Air Quality
The health stakes are significant. Fine inhalable particulate matter, known as PM 2.5, can lodge deep in the lungs, while even smaller ultrafine particles (PM 0.1) can enter the bloodstream. According to NPR, current air quality index (AQI) values in many areas have reached the “hazardouslevel of at least 301, a range the EPA describes as
extremely rare.”
Even when outdoor conditions improve, the threat to indoor air may persist.
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