What size air purifier do I need for wildfire smoke in a 400 sq ft room?

A smoke CADR of 400. AHAM, which runs the CADR test, says that for wildfire smoke the smoke CADR should equal the room's square feet. EPA's everyday chart asks for about 260 for 400 sq ft, so a 260 unit is the bare minimum. Of the 30 certified purifiers we could buy on Amazon today, only the Fellowes AeraMax SV reaches 400 alone; two KNKA APH4000 units reach 452.

Which CADR number matters for smoke?

Smoke CADR. EPA: "choose a portable air cleaner that has a high CADR for tobacco smoke, which represents the smallest particles." Wildfire smoke is mostly these fine particles. Dust and pollen CADR measure bigger particles and run higher, so they flatter a purifier.

Is the room size on the Amazon listing real?

Not for smoke. Many listings quote the room a purifier can clean once an hour. The Wozoyo Pure Air PA2 listing says up to 563 sq ft; AHAM certifies it for 116 sq ft, and in wildfire smoke it covers about 75. Use the AHAM smoke CADR, not the box.

Do I need a carbon filter for smoke smell?

For the smell, yes; for the particles, no. The smell is gas, and EPA says "The CADR rating system is for particles only." It also says carbon filters work "provided that there is a large amount of material used in the filter." A thin carbon layer helps a little.

Are ionizers or ozone air purifiers safe in smoke?

Skip anything that makes ozone. EPA: "Avoid portable air cleaners ... that intentionally produce ozone. Ozone is a lung irritant." Check the California Air Resources Board (CARB) list of tested air cleaners. Every purifier we pick is on it.

How often should I change the filter during smoke season?

More often than the box says. EPA: "During periods of heavy smoke, plan to replace the filter in your air cleaner or HVAC system more often than recommended by the manufacturer." Keep a spare filter on hand before fire season.

Does a DIY box fan air purifier really work for smoke?

Yes, as a stopgap. EPA tested box fans with MERV 13 filters: one 1-inch filter cleaned 111 CFM of smoke, and a Corsi-Rosenthal box (four filters and a cardboard shroud) cleaned 401. EPA says to use a 2012-or-newer fan, never leave children alone with it, skip extension cords, and treat it as temporary.

Should I run my air purifier all the time during wildfire smoke?

Yes. EPA says to set up one clean room, close its windows and doors, and "Run the portable air cleaner continuously on the highest fan setting if you can." A bedroom with its own bathroom works well.

Does an air purifier protect me from wildfire gases or carbon monoxide?

No. Purifiers catch particles; CADR does not measure gases. Follow evacuation orders, and use a carbon monoxide alarm.

Best Air Purifier for Wildfire Smoke (2026): Picks by Room Size

For a bedroom or living room up to about 391 sq ft, buy the Levoit Core 600S. In wildfire smoke, AHAM says your purifier's smoke CADR should equal the room's square feet; the 600S's is 391.

Best for most rooms in smoke

Levoit Core 600S

$259.97 on Amazon

Check price on Amazon

AHAM-certified smoke CADR of 391: enough for a 391 sq ft room in wildfire smoke, or 606 sq ft on a normal day.
The most smoke cleaning per dollar of the 4 purifiers we could buy today that clear a 300 sq ft room in smoke.
On California's (CARB) list of air cleaners tested for ozone and electrical safety. ENERGY STAR, 65.6 W.
Genuine filter: $59.99, changed every 6–12 months by the maker's schedule: about $120 a year.

Which one is right for you?

For a small bedroom (up to about 226 sq ft)
KNKA APH4000 · 226 smoke CADR · HEPA-type + carbon
The cheapest purifier we found that meets AHAM's wildfire rule for a 200 sq ft room.
$99.99 on Amazon
For a 400 sq ft room
Two KNKA APH4000 purifiers · 226 smoke CADR each · HEPA-type + carbon
Together 452 smoke CADR, the cheapest way we found to meet AHAM's wildfire rule for 400 sq ft. The only single unit that does it, the Fellowes AeraMax SV, costs $735. After smoke season, split them between two rooms.
$99.99 each on Amazon
For a large or open room (up to about 726 sq ft)
Two Wozoyo Pure Air PA6 purifiers · 363 smoke CADR each · True HEPA + carbon
Together 726 smoke CADR. Put them at opposite ends of the room and run both on high.
$249.99 each on Amazon
Cheapest for a small room
Dreo 338 · 115 smoke CADR · True HEPA
Enough for about 115 sq ft in smoke (a small bedroom or nursery), 178 sq ft on normal days.
$59.98 on Amazon
Do it yourself: a box-fan filter (EPA tested)
MERV 13 filters, 20 × 20 × 1, 4-pack · Four filters for a Corsi-Rosenthal box: EPA measured 401 smoke CADR
Tape the four filters into a cube on a 20-inch box fan made in 2012 or later, with a cardboard shroud. EPA calls it a temporary fix: use a real purifier when you can. It is also loud.
$37.99 on Amazon

Prices are Amazon's on November 11, 2026. Room sizes in smoke use AHAM's wildfire rule: smoke CADR = square feet.

By Erin Rose · Updated November 11, 2026

01 / Size

How big a purifier you need for smoke

Buy on smoke CADR, the number AHAM certifies. EPA says smoke CADR stands for "the smallest particles," the kind in wildfire smoke.

On a normal day, AHAM and EPA ask for a smoke CADR of at least two-thirds of the room's square feet. In wildfire smoke, AHAM asks for more: a smoke CADR equal to the square feet. Rooms with ceilings over 8 feet need more still.

Smoke CADR needed by room size, and how many purifiers we could buy today reach it
Room	Normal day (EPA)	Wildfire smoke (AHAM)	Units that reach it	Cheapest today
150 sq ft	98	150	19 of 30	KNKA APH4000 · $99.99
200 sq ft	130	200	19 of 30	KNKA APH4000 · $99.99
300 sq ft	195	300	4 of 30	Wozoyo Pure Air PA6 · $249.99
400 sq ft	260	400	1 of 30	Fellowes AeraMax SV · $735
500 sq ft	325	500	1 of 30	Fellowes AeraMax SV · $735
600 sq ft	390	600	0 of 30	None alone; use two

Smoke CADR needed. Normal day = EPA's chart (65 per 100 sq ft). Wildfire smoke = AHAM's rule (smoke CADR equal to the square feet). 8-foot ceilings.

02 / Smoke

What else matters in smoke

Run it on high, in one closed room.EPA: "Run the portable air cleaner continuously on the highest fan setting if you can." Pick a room you can close off, like a bedroom with its own bathroom.
Carbon for the smell, not the particles.EPA: "The CADR rating system is for particles only." Carbon works on gases "provided that there is a large amount of material used in the filter."
No ozone.EPA: "Avoid portable air cleaners ... that intentionally produce ozone." Ionizers and plasma units can make some. CARB tests air cleaners for ozone; every pick here is on its list.
Spare filters.EPA: plan to replace filters "more often than recommended by the manufacturer" during heavy smoke. Buy a spare before fire season.

03 / Box fan

EPA's box-fan purifier: what it really cleans

EPA tested box fans with MERV 13 furnace filters in a smoke chamber. More filters and a cardboard shroud made a big difference.

Smoke CADR EPA measured for each box-fan design

One 1" MERV 13 filter111
One 1" filter + cardboard shroud156
One 4" filter + shroud248
Two 1" filters + shroud263
Corsi-Rosenthal box: four 1" filters + shroud401

Cubic feet per minute of smoke-free air, 20-inch box fan, MERV 13 filters. Source: U.S. EPA.

Safety, in EPA's words: use a fan "built in 2012 or more recently" with a UL or ETL mark, "do not leave children unattended," and "do not use an extension cord." EPA calls DIY units "a temporary alternative to commercial air cleaners."

04 / Every one in stock

All 30 certified purifiers we could buy today

All 30 certified purifiers we could buy today: smoke CADR, room size on a normal day, filter and Amazon price
Purifier	Smoke CADR = sq ft in smoke	Room, normal day	Filter	Price	Buy
Clears 400+ sq ft in wildfire smoke
Fellowes AeraMax SVsold by Amazon	518	803 sq ft	—	$735	Buy
Clears 300 to 399 sq ft in smoke
Levoit Core 600Ssold by Amazon	391	606 sq ft	HEPA-type	$259.97	Buy
Wozoyo Pure Air PA6	363	563 sq ft	True HEPA + carbon	$249.99	Buy
Whirlpool WPPRO2000	341	529 sq ft	True HEPA	$349.99	See Winix 9800 on Amazon
Clears 200 to 299 sq ft in smoke
Dreo Macro Max ASsold by Amazon	294	456 sq ft	True HEPA	$149.99	Buy
Blueair Blue Pure 311i Maxsold by Amazon	283	439 sq ft	Fabric	$149.99	See Winix AT40 on Amazon
Winix T810sold by Amazon	270	418 sq ft	True HEPA	$175.99	Buy
Winix AT40sold by Amazon	265	410 sq ft	True HEPA + carbon	$192.57	Buy
Winix 5510sold by Amazon	253	392 sq ft	True HEPA + carbon	$179.99	Buy
Winix 5520sold by Amazon	253	392 sq ft	True HEPA + carbon	$179.99	See Winix AT40 on Amazon
Winix 5530sold by Amazon	253	392 sq ft	True HEPA + carbon	$219.99	See Winix AT40 on Amazon
Levoit Vital 200Ssold by Amazon	250	388 sq ft	HEPA-type	$169.96	Buy
Winix C610	248	384 sq ft	True HEPA	$176.49	Buy
Honeywell HPA4300Bsold by Amazon	229	354 sq ft	True HEPA	$158.11	Buy
KNKA APH4000	226	350 sq ft	HEPA-type + carbon	$99.99	Buy
GermGuardian AC3200sold by Amazon	225	348 sq ft	True HEPA	$229.99	Buy
GermGuardian AC3250sold by Amazon	224	347 sq ft	True HEPA	$239.99	Buy
GermGuardian AP3250sold by Amazon	222	345 sq ft	True HEPA	$229.99	Buy
Blueair DustMagnet 5440isold by Amazon	216	335 sq ft	HEPA-type + carbon	$319.99	See Winix AT40 on Amazon
Under 200 sq ft in smoke
Dreo DR-HAP009ASsold by Amazon	145	225 sq ft	True HEPA	$107.93	Buy
Levoit Core 300sold by Amazon	143	222 sq ft	HEPA-type	$84.99	Buy
Levoit Vital 100Ssold by Amazon	143	222 sq ft	HEPA-type	$113.99	Buy
Whirlpool WPT80	129	199 sq ft	True HEPA	$149.29	Buy
GermGuardian AC5250PTsold by Amazon	122	189 sq ft	True HEPA	$149.99	Buy
Dreo 338sold by Amazon	115	178 sq ft	True HEPA	$59.98	Buy
GermGuardian AC4825Esold by Amazon	99	153 sq ft	True HEPA	$124	Buy
GermGuardian AC4300sold by Amazon	89	138 sq ft	True HEPA	$99.99	See KNKA on Amazon
Wozoyo Pure Air PA2	75	116 sq ft	True HEPA + carbon	$67.99	Buy
Whirlpool WPT60 (black)	70	108 sq ft	True HEPA	$106.69	Buy
Levoit Core Minisold by Amazon	34	53 sq ft	HEPA-type	$39.99	Buy

Smoke CADR and room size (normal day) are AHAM-certified. In wildfire smoke, a purifier covers as many square feet as its smoke CADR (AHAM's rule). Filter type is how AHAM files it; a dash means AHAM does not list it. Listings in a paid campaign are left out. Prices read live November 11, 2026. See every certified unit, in stock or not, on our main purifier guide.

05 / Questions

Frequently asked

What size air purifier do I need for wildfire smoke in a 400 sq ft room?: A smoke CADR of 400. AHAM, which runs the CADR test, says that for wildfire smoke the smoke CADR should equal the room's square feet. EPA's everyday chart asks for about 260 for 400 sq ft, so a 260 unit is the bare minimum. Of the 30 certified purifiers we could buy on Amazon today, only the Fellowes AeraMax SV reaches 400 alone; two KNKA APH4000 units reach 452.
Which CADR number matters for smoke?: Smoke CADR. EPA: "choose a portable air cleaner that has a high CADR for tobacco smoke, which represents the smallest particles." Wildfire smoke is mostly these fine particles. Dust and pollen CADR measure bigger particles and run higher, so they flatter a purifier.
Is the room size on the Amazon listing real?: Not for smoke. Many listings quote the room a purifier can clean once an hour. The Wozoyo Pure Air PA2 listing says up to 563 sq ft; AHAM certifies it for 116 sq ft, and in wildfire smoke it covers about 75. Use the AHAM smoke CADR, not the box.
Do I need a carbon filter for smoke smell?: For the smell, yes; for the particles, no. The smell is gas, and EPA says "The CADR rating system is for particles only." It also says carbon filters work "provided that there is a large amount of material used in the filter." A thin carbon layer helps a little.
Are ionizers or ozone air purifiers safe in smoke?: Skip anything that makes ozone. EPA: "Avoid portable air cleaners ... that intentionally produce ozone. Ozone is a lung irritant." Check the California Air Resources Board (CARB) list of tested air cleaners. Every purifier we pick is on it.
How often should I change the filter during smoke season?: More often than the box says. EPA: "During periods of heavy smoke, plan to replace the filter in your air cleaner or HVAC system more often than recommended by the manufacturer." Keep a spare filter on hand before fire season.
Does a DIY box fan air purifier really work for smoke?: Yes, as a stopgap. EPA tested box fans with MERV 13 filters: one 1-inch filter cleaned 111 CFM of smoke, and a Corsi-Rosenthal box (four filters and a cardboard shroud) cleaned 401. EPA says to use a 2012-or-newer fan, never leave children alone with it, skip extension cords, and treat it as temporary.
Should I run my air purifier all the time during wildfire smoke?: Yes. EPA says to set up one clean room, close its windows and doors, and "Run the portable air cleaner continuously on the highest fan setting if you can." A bedroom with its own bathroom works well.
Does an air purifier protect me from wildfire gases or carbon monoxide?: No. Purifiers catch particles; CADR does not measure gases. Follow evacuation orders, and use a carbon monoxide alarm.

References

Sources

9 references · prices on November 11, 2026

1
AHAM Verifide: Air Filtration Standards (the 2/3 rule and the wildfire-smoke rule)

Read October 20, 2026. "For wild fire smoke, AHAM recommends a Smoke CADR equal to the size of the room in square feet."
2
AHAM Verifide directory of certified room air cleaners

Smoke, dust and pollen CADR, certified room size and ENERGY STAR for every purifier on this page.
3
U.S. EPA: Guide to Air Cleaners in the Home

Read October 20, 2026. Sizing chart (65 CADR per 100 sq ft), smoke CADR for the smallest particles, carbon for gases, avoid ozone.
4
U.S. EPA: Create a clean room to protect indoor air quality during a wildfire

Read October 20, 2026. Close one room, run the purifier on high, change filters more often in heavy smoke.
5
U.S. EPA research: DIY air cleaners to reduce wildfire smoke indoors

Read October 20, 2026. Lab smoke CADR: one 1" MERV 13 filter 111; Corsi-Rosenthal box with four filters and a shroud 401.
6
U.S. EPA: DIY air cleaners (fan safety)

Read October 20, 2026. Use a 2012-or-newer box fan with a UL or ETL mark.
7
California Air Resources Board: list of CARB-certified air cleaning devices

Read October 20, 2026. Certification covers ozone (0.050 ppm limit) and electrical safety, not cleaning performance.
8
Maker filter pages: replacement intervals

Each maker's own page or manual, read October 20, 2026.
9
Amazon listings: price, seller and stock

Read live on November 11, 2026. A price shows only if the listing could be bought that day.