The short answer
Yes, for the fine particles in smoke. Across studies done during real wildfire and wood-smoke events, running a portable air cleaner indoors lowered PM2.5 (the fine particulate that makes smoke harmful) by an average of about 56%, though individual results ranged from about 5% to 99%. The evidence is weaker on two other questions people care about: whether purifiers remove smoke gases and odors, and whether they measurably improve health. Those answers are still uncertain.
What the evidence shows
The most complete recent summary is a 2025 rapid systematic review from Canada's National Collaborating Centre for Environmental Health (NCCEH). It found 30 relevant studies. Its main conclusions:
- Particles: Air cleaning during smoke episodes may reduce indoor PM2.5 by 56% on average. The reviewers rated their certainty in the size of that effect as low, because study methods and devices varied widely.
- Indoor/outdoor ratio: The average ratio of indoor to outdoor PM2.5 fell from about 0.69 to 0.37 with air cleaning.
- Gases: There was not enough evidence to judge how well filtration removes gases such as VOCs. In two lab studies, only devices with activated carbon filters reduced them, and the results were inconsistent.
- Health: The evidence is uncertain on health benefits. Only four studies measured health outcomes, and results were mixed.
In plain terms: the evidence that purifiers clean smoke particles from indoor air is reasonably consistent. The evidence that they improve how you feel or reduce hospital visits is thin.
Individual studies
| Study | Setting | Result |
|---|---|---|
| Xiang et al., 2021 (Science of the Total Environment) | 7 homes in Seattle during the 2020 wildfire episode | HEPA purifiers in auto mode cut indoor PM2.5 by 48 to 78%. Smoke leaked in even with windows closed, so staying inside alone did not prevent exposure. |
| Stauffer et al., 2020 (Journal of Occupational and Environmental Hygiene) | Two identical offices, one with a purifier | Indoor PM2.5 was reduced by 73% during working hours and 92% outside working hours. |
| EPA field pilot, Hoopa, California (2021) | 6 homes, DIY box-fan filter vs. commercial purifier | Both reduced indoor PM2.5. The DIY unit was loud, which discouraged people from running it. Very small study. |
Why room size and CADR matter
The NCCEH review noted that studies which matched the purifier's clean air delivery rate (CADR) to the size of the room cleaned the air more effectively. CADR measures how much filtered air a unit delivers per minute. This is why our calculator compares smoke CADR against room area instead of relying on the room-size claim printed on the box.
A common rule of thumb is that smoke CADR should be at least two-thirds of your floor area in square feet, assuming 8-foot ceilings. For a 400 sq ft room, that means a smoke CADR of roughly 267 or higher. Our sizing guide has a full table.
What purifiers do not solve
- Smoke gases and odors. HEPA filters trap particles, not gases. Activated carbon is the only filter type with lab evidence for reducing smoke VOCs, and the amount of carbon matters. See HEPA vs. carbon filters.
- Leaky homes. In the Seattle study, the share of outdoor PM2.5 that got inside varied from about a third to three-quarters depending on the home. A purifier works against that leakage but does not stop it.
- Ozone-producing devices. Some air cleaners generate ozone, which is a lung irritant. The NCCEH review notes the EPA's warnings about harmful by-products from some technologies. Stick with mechanical filtration.
What to do during a smoke event
- Close windows and doors, and run the purifier in the room where you spend the most time.
- Use auto mode if your unit has it. The Seattle study used auto-mode units.
- Choose a unit whose smoke CADR fits your room (see above).
- Keep spare filters on hand. Heavy smoke loads filters faster than normal use.
- If you cannot afford a purifier, a box fan with a MERV 13 filter has some supporting research, but it is noisier and less studied. See DIY box-fan cleaners.
What we will test next
The published research tells us what purifiers do in general. It does not tell you which specific models do it best for the money. We are planning our own measurements of PM2.5 removal and noise, and we will add the results here when they are done.
Sources
- NCCEH and NCCMT. Indoor air filtration during wildfires: Impacts on air quality and health (rapid review, 2025). ncceh.ca
- Xiang J, et al. Field measurements of PM2.5 infiltration factor and portable air cleaner effectiveness during wildfire episodes in US residences. Science of the Total Environment 773:145642 (2021). doi.org/10.1016/j.scitotenv.2021.145642
- Stauffer DA, et al. Control of wildfire-sourced PM2.5 in an office setting using a commercially available portable air cleaner. Journal of Occupational and Environmental Hygiene 17(4):109-120 (2020). doi.org/10.1080/15459624.2020.1722314
- U.S. EPA. Impact of do-it-yourself and commercial air cleaner usage on health and residential PM2.5 (Hoopa pilot study summary). assessments.epa.gov
- Barn P, et al. Portable air cleaners should be at the forefront of the public health response to landscape fire smoke. Environmental Health 15:116 (2016). pmc.ncbi.nlm.nih.gov