Air Quality · Buying guide
Air Purifier Buying Guide: HEPA, CADR, Carbon and Room Size
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A portable air purifier is one of the few home purchases where the right size matters more than the brand. Match the clean air delivery rate to your room, budget for filters, and choose carbon if smoke or odors are the problem.
Purifiers worth a look
| Model | Filtration | Maker's coverage claim | Filter life (maker) | Warranty (maker) | Where |
|---|---|---|---|---|---|
| Austin Air HealthMate (HM400) | Pre-filters, about 15 lb of activated carbon and zeolite, 60 sq ft of medical-grade HEPA | Up to 1,500 sq ft | Up to 5 years | 5 years on the unit; 5-year pro-rated on the filter | Austin Air |
| PuroAir 400 | Pre-filter, HEPA and activated carbon; air-quality sensor and auto mode | Up to 2,000 sq ft cleaned in about an hour | Replace per the filter light (typically several months) | 2 years; lifetime with filter subscription | PuroAir |
| PuroAir 240 | Same 3-layer system, smaller | Up to 1,000 sq ft in about an hour | Per the filter light | 2 years | PuroAir |
| Many brands, one store | Air purifiers, dehumidifiers and replacement filters | Varies | Varies | Varies | Sylvane |
Specs from Austin Air and PuroAir product pages and FAQs, October 2026. Prices change often; check the current price.
Buy right once: Size by CADR, not by the "up to" square footage on the box. Price out three years of filters before you buy, because a cheap purifier with expensive filters isn't cheap.
Before you buy, check:
- Room size in square feet and ceiling height
- Smoke CADR (or the maker's tested air changes per hour)
- Filter price and replacement interval
- Noise on the setting you'll actually use
Austin Air HealthMate is the heavy-duty choice. It's a steel unit with a very large carbon and zeolite bed, which is what adsorbs smoke odor, gases and VOCs. A thin carbon sheet can't do that for long. The filter is designed to last up to five years, so running costs are low even though the unit costs more up front. It's big (about 23 inches tall and 14.5 inches wide) and has a simple three-speed fan with no app.
PuroAir 400 is lighter (about 14.7 lb), quieter at its lowest setting (PuroAir lists 31 dB) and has an air-quality sensor that ramps the fan automatically. Its coverage claims are based on about one air change per hour, which is less than allergy-focused guidance recommends, so treat 2,000 sq ft as the absolute top end (see sizing below).
Sylvane is a specialty retailer for air purifiers, dehumidifiers, humidifiers and replacement filters from many brands. It's useful for comparing models from different makers in one place and for finding filters for an older purifier.
CADR and room size
CADR (clean air delivery rate) is measured under the AHAM AC-1 standard in cubic feet per minute for smoke, dust and pollen. Smoke particles are the smallest and hardest to catch, so the smoke CADR is the most useful single number. AHAM's rule of thumb is that the smoke CADR should be at least two-thirds of the room's area in square feet, for an 8-foot ceiling. That works out to roughly five air changes per hour.
| Room (8 ft ceiling) | Area | Minimum smoke CADR (2/3 rule) | For wildfire smoke or allergies |
|---|---|---|---|
| Small bedroom | 120 sq ft | 80 CFM | 100+ CFM |
| Main bedroom | 200 sq ft | 130 CFM | 170+ CFM |
| Living room | 350 sq ft | 235 CFM | 300+ CFM |
| Open-plan great room | 600 sq ft | 400 CFM | Two purifiers or one large unit |
For taller ceilings, scale up: a 10-foot ceiling has 25% more air than an 8-foot one. Running a purifier on a quieter, lower setting cuts its delivery rate a lot, so a unit that's oversized for the room can run quietly and still keep up.
Not every maker publishes AHAM CADR. Austin Air quotes about 400 CFM on high for the HealthMate, and PuroAir reports independent-lab coverage and air changes instead. Where there's no smoke CADR, compare the maker's tested air changes per hour for your room size.
HEPA, carbon and what to avoid
| Technology | What it removes | Notes |
|---|---|---|
| True HEPA | Particles: dust, pollen, pet dander, smoke particles, most mold spores | Captures at least 99.97% of 0.3-micron particles under the U.S. standard. "HEPA-type" or "HEPA-like" isn't the same thing. |
| Activated carbon | Gases and odors: smoke smell, cooking, VOCs | The amount matters. A few ounces saturate quickly; several pounds last. |
| Zeolite | Some gases such as ammonia | Often blended with carbon (Austin Air) |
| Ionizers / ozone generators | Charge particles so they settle | Ozone irritates lungs. California limits ozone emissions from air cleaners; avoid ozone generators. |
| UV-C | Claimed to inactivate microbes | Short exposure inside a purifier has limited proven benefit; don't pay extra for it. |
The EPA's guidance on portable air cleaners makes the same points: choose by CADR for your room, use HEPA filtration for particles, and avoid air cleaners that intentionally produce ozone.
Filter costs over three years
Filters are the real cost of owning a purifier. Before you buy, multiply the replacement filter price by the number of changes in three years of the way you'll run it. A purifier on 24/7 during wildfire season will need filters sooner than the box says.
| Filter pattern | Changes in 3 years | What to compare |
|---|---|---|
| Long-life combined filter (Austin Air, up to 5 years) | 0–1 | Higher unit price, very low running cost |
| Combined HEPA + carbon cartridge, changed every 6 months | About 6 | Cartridge price x 6, or the subscription price |
| Separate pre-filter, HEPA and carbon | Varies by layer | Washable pre-filters save money |
Noise and placement
- Bedrooms: look for a low setting around 30 dB or less and a way to dim the lights. Oversize the purifier so the quiet setting is enough.
- Placement: keep a foot or two of clearance on the intake sides, away from curtains. Running it near where you sit or sleep helps more than tucking it in a corner.
- Doors and windows: close them during smoke events, or the purifier is trying to clean the outdoors.
- Run it continuously on a low or auto setting rather than on high for an hour now and then.
- Central air: a MERV 13 filter in your HVAC system, with the fan running, is another good way to clean a whole house during smoke events. See our heat pump guide for HVAC basics.
FAQ
Do air purifiers help with allergies?
A HEPA purifier reduces airborne allergens like pollen and pet dander, especially in a closed bedroom. It doesn't remove allergens settled in carpets and bedding, so cleaning still matters.
Can an air purifier remove wildfire smoke?
HEPA filters capture the fine smoke particles, and carbon helps with the smell. Size for at least the 2/3 rule in the room you're using, close the windows, and expect to change filters sooner.
Is one big purifier better than two small ones?
For separate rooms, two units work better because air doesn't move well between rooms through doorways. For one large open space, a single large unit is usually quieter per CFM.
Sources
- AHAM, Verifide air cleaner program and the 2/3 CADR rule: ahamverifide.org
- U.S. EPA, Guide to Air Cleaners in the Home: epa.gov
- Austin Air, FAQ (filter media, 5-year filter life and warranty): austinairsystems.com
- PuroAir, PuroAir 400 product page and FAQs (coverage, weight, noise, warranty): getpuroair.com
- California Air Resources Board, air cleaner ozone limits: arb.ca.gov