How do you set up a clean-air room at home?

Short answer. Pick one room big enough for everyone, close its windows and doors without blocking your way out, and run an air cleaner that does not produce ozone, continuously, on its highest setting ¹. Size it so its tobacco-smoke CADR is at least two-thirds of the room's area in square feet ²⁶. Set any air conditioning to recirculate, and stay in the room as much as you can ¹².

What is a clean-air room, and when should you use one?

A clean-air room is one room in your home where you keep the levels of smoke and fine particles as low as possible while the outdoor air is bad. The U.S. EPA calls it a "cleaner air room" and says anyone can benefit from spending time in one during a smoke event ². The CDC's advice is the same idea in one line: choose a room you can close off from outside air and set up a portable air cleaner or a filter in it ⁷.

The EPA and the CDC describe it for wildfire smoke ¹⁷. For the health effects of smoke and the U.S. and Canadian alert scales, see the Phaenyx guide on wildfire smoke; for ashfall, see the guide on volcanic ash.

The EPA's advice applies only as long as it is safe to stay home ². If you are told to evacuate, leave.

Not the same as chemical shelter-in-place. A clean-air room keeps air moving through a filter and is aired out as soon as the outdoor air improves ¹. A chemical release calls for different steps, covered in the guide on chemical shelter-in-place.

Which room should you choose?

The EPA suggests a room that fits everyone in the household and is comfortable for long periods; a bedroom with an attached bathroom works well because it can stay closed ¹. The CDC says to choose a room you can close off from outside air ⁷. The EPA suggests placing the air cleaner in the room you spend the most time in, and notes that in an open floor plan it has to serve the whole open space ³.

Close windows and doors, but do not do anything that makes it hard to leave the room in an emergency ². Use bathroom fans or range hoods only briefly, because they can pull smoke in from the rest of the home ¹.

How big an air cleaner does the room need?

The EPA and Health Canada give the same rule: the tobacco-smoke clean air delivery rate (CADR) should be at least two-thirds of the room's floor area in square feet ²⁶. Health Canada's example: a 120 sq ft room needs a smoke CADR of at least 80 ⁶. The EPA's chart assumes an 8-foot ceiling and says higher ceilings call for a higher CADR ³.

If your unit is rated in m³/h, the same rule works out to roughly 12 m³/h of smoke CADR per square metre of floor, for a ceiling of about 2.4 m. Portable cleaners often reach a high CADR with a HEPA filter ³⁶. Health Canada advises the highest smoke CADR your budget allows ⁶.

Run it continuously on the highest fan setting ¹; higher fan speeds and longer run times filter more air ³. Place it where nothing blocks the airflow ³, and, per Health Canada, so it does not blow directly at or between people ⁶.

Can a box fan with a furnace filter replace a purifier?

As a stopgap, yes. The EPA calls a DIY box-fan cleaner a temporary option when you cannot afford or find a portable air cleaner, not a permanent substitute ¹. Its laboratory tests show how much the design matters ⁴:

The shroud alone raised CADR by 40% at no added cost ⁴. Dirty filters made DIY units nearly ineffective, so replace them often during smoke, as often as every few days or weeks ⁴¹. Use MERV 13 or higher, with the airflow arrows pointing the right way and a good seal ¹.

Safety limits. In testing for the EPA, none of the fan-and-filter set-ups caught fire, but results may not apply to every fan ⁴. The EPA's conditions ⁴¹:

• use only box fans built in 2012 or later, with a UL or ETL safety mark; they have fused plugs and thermal cutoffs;
• do not use an older fan unattended or while sleeping;
• do not use an extension cord;
• do not leave children unattended with the fan running.

How should you set the air conditioning or ventilation?

Stay cool with fans, window air conditioners or central air ¹. If your system brings in fresh air, turn that option off or close the intake and run it in recirculation mode ². With central air, a MERV 13 or higher filter helps, and setting the fan to "On" instead of "Auto" filters more air; a technician can confirm your system takes that filter ¹.

Evaporative coolers need care: the EPA says to cover their outside intakes with 4-inch MERV 13 filters or use them sparingly ¹, and to use single-hose portable air conditioners sparingly ¹. If heat becomes a danger, the room has failed its purpose: the EPA says to go elsewhere, such as to family, a public clean-air shelter or a large building with good filtration ¹.

What should you not do in the room?

• Do not use an ozone generator. No U.S. federal agency has approved them for occupied spaces ⁵. Ozone can damage the lungs, and relatively low amounts can cause chest pain, coughing and shortness of breath ⁵. It does not remove particles ⁵. The EPA also lists ionizers and electrostatic precipitators among devices that may emit ozone ³.
• Do not add particles: no smoking or vaping, candles or incense, gas, propane or wood stoves, aerosol sprays, frying or broiling ¹.
• Do not vacuum unless the vacuum has a HEPA filter; dust and mop with a damp cloth instead ¹.
• Do not exercise in the room, to reduce your exposure to any particles that get in ¹.

When the outdoor air improves, air the room out: open windows or the fresh-air intake and run the kitchen and bathroom fans ¹.

Who needs the room most?

The EPA says a cleaner air room may help most for people with heart or lung disease, older adults, children and pregnant people ². The CDC adds people with asthma, COPD or diabetes ⁷. Give them the room first. The EPA advises people with heart or lung disease, including asthma, to check with their health care provider about what to do during smoke events ¹. EPA Victoria says to call emergency services if anyone has trouble breathing, chest pain or tightness in the chest ⁸.

What official agencies recommend

• United States (EPA, CDC). Close off one room, filter it with a correctly sized, ozone-free portable cleaner, recirculate air conditioning and avoid indoor sources ¹²⁷. DIY box-fan cleaners are a temporary option only ¹.
• Canada (Health Canada). Smoke CADR of at least two-thirds of the room area, the highest your budget allows; avoid ozone-producing devices ⁶.
• Australia (EPA Victoria). Use a portable HEPA air cleaner if you have one and switch air conditioners to recirculate ⁸.

Where they differ. On evaporative coolers, EPA Victoria says to avoid them because they pull outside air in ⁸, while the U.S. EPA allows them with MERV 13 filters over the intakes or sparing use ¹. On placement, Health Canada adds that the cleaner should not blow directly at or between people ⁶.

Frequently asked questions

Do I need to tape the windows shut?

No. The EPA's steps are to close windows and doors without making it hard to leave the room ². Sealing a room is a different procedure, covered in the guide on chemical shelter-in-place.

Should I run the air cleaner at night?

Yes, continuously and on the highest setting if you can ¹. If you use a DIY fan built before 2012, the EPA says not to run it while sleeping ⁴.

Can I use the room during a city pollution episode, not just fires?

The EPA writes its cleaner-air-room steps for wildfire smoke, describing a room that keeps "smoke and other pollutants" as low as possible ². The filtering itself is not specific to fires: an air cleaner's tobacco-smoke CADR measures how well it removes small particles ³. Follow your local air-quality alerts for timing.

Air risks are not the same everywhere; see what applies where you live, country by country, on /air.

Your plan, ready before the smoke

Your Phaenyx plan's "Water and air" section lists the water and air risks for your postal code, so you know which events to set up this room for. The Phaenyx Safe app keeps the reflex sheets, including this one, available offline. Build your Phaenyx plan.

Sources

1. U.S. Environmental Protection Agency (EPA) — Create a Clean Room to Protect Indoor Air Quality During a Wildfire — https://www.epa.gov/indoor-air-quality-iaq/create-clean-room-protect-indoor-air-quality-during-wildfire (accessed 2026-10-27)
2. U.S. Environmental Protection Agency (EPA) — How to Create a Cleaner Air Room at Home — https://www.epa.gov/wildfires/how-create-cleaner-air-room-home (accessed 2026-10-27)
3. U.S. Environmental Protection Agency (EPA) — Guide to Air Cleaners in the Home — https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home (accessed 2026-10-27)
4. U.S. Environmental Protection Agency (EPA) — Research on DIY Air Cleaners to Reduce Wildfire Smoke Indoors — https://www.epa.gov/air-research/research-diy-air-cleaners-reduce-wildfire-smoke-indoors (accessed 2026-10-27)
5. U.S. Environmental Protection Agency (EPA) — Ozone Generators that are Sold as Air Cleaners — https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners (accessed 2026-10-27)
6. Health Canada — Using a portable air cleaner to improve indoor air — https://www.canada.ca/en/health-canada/services/publications/healthy-living/using-portable-air-cleaner-wildfire-smoke.html (accessed 2026-10-27)
7. Centers for Disease Control and Prevention (CDC) — Preparing for Wildfires — https://www.cdc.gov/wildfires/safety/index.html (accessed 2026-10-27)
8. Environment Protection Authority Victoria (Australia) — Managing health impacts from bushfire smoke — https://www.epa.vic.gov.au/managing-health-impacts-bushfire-smoke (accessed 2026-10-27)