Equipment
Filtration that actually works
Filtration is the third step, after stopping the source and ventilating. It is genuinely effective against particles: wildfire smoke, cooking aerosols, dust, pollen and mould spores are all things a decent filter removes from a room.
It does nothing at all for gases. Radon, carbon monoxide and nitrogen dioxide pass through a HEPA filter untouched, and no amount of money spent on a purifier changes that. Knowing which of your problems is a particle and which is a gas is most of the decision.
The scale
What MERV ratings actually capture
| Rating | Captures | In practice |
|---|---|---|
| MERV 1-4 | Coarse dust, lint, carpet fibres | Protects the equipment, not you |
| MERV 5-8 | Mould spores, dust mite debris, hair spray | Common builder-grade filter |
| MERV 9-12 | Fine dust, some PM2.5, humidifier dust | A reasonable home minimum |
| MERV 13-16 | Bacteria, smoke, most PM2.5, sneeze particles | What to fit for smoke or allergies |
| HEPA | ≥99.97% of 0.3 µm particles | Portable units and true HEPA systems only |
MERV is the ASHRAE 52.2 Minimum Efficiency Reporting Value. HEPA is defined by efficiency at the most-penetrating particle size, conventionally 0.3 µm. Guidance on fitting MERV 13 follows EPA and ASHRAE recommendations for improving indoor air quality.
Sizing
Read the CADR, not the marketing square footage
CADR - clean air delivery rate - is the honest number on a purifier box. It is measured under the AHAM standard and reported separately for smoke, dust and pollen. The smoke figure is the one to use, because smoke particles are the smallest of the three and therefore the hardest to capture.
The rule of thumb: smoke CADR ≥ two thirds of the room’s floor area in square feet. A 300 sq ft bedroom wants a smoke CADR of about 200. That delivers roughly five air changes an hour in a room with a standard ceiling.
Two practical points that matter more than the model you choose. A purifier only cleans the room it is in, so one large unit for an open-plan area and a small one for the bedroom beats a single machine moved around. And every unit is much quieter and much less effective on its lowest setting, so buy one big enough to run on medium.
Avoid
The categories not to buy
Ozone generators
Sold as air purifiers, they work by producing a lung irritant that is itself a regulated outdoor pollutant. California restricts the sale of indoor air cleaners emitting ozone above a set limit. There is no configuration in which this is a good idea in an occupied room.
Purifiers bought for radon
The single most common expensive mistake in this category. Radon is a gas; filtration is irrelevant to it. Money spent here is money not spent on a mitigation system.
Ultra-restrictive filters in a system that cannot move air through them
A MERV 16 filter in a furnace designed for MERV 8 starves the blower, cuts airflow and can ice the coil. Check the pressure drop your system tolerates, or use a deeper pleated filter with more surface area at the same rating.
Anything sold on a claim about your lungs
Devices marketed as treating, preventing or reversing a respiratory condition are making a medical claim. Filtration removes particles from a room. That is a real and useful thing, and it is all any of them do.
Equipment
Purifiers and filters
HEPA air purifiers
Affiliate linksMatch the smoke CADR to the room: roughly two thirds of the floor area in square feet. Removes particles; does nothing for radon or any other gas.
MOOKA
MOOKA Air Purifier for Home Bedroom Large Room 2200 Ft², True HEPA Filter
ECOSELF
Air Purifier for Large Room, Cleans 2,400 ft² in 30 Mins, 3-Stage True HEPA, 360° Airflow, Large Touch Display Control, Real-Time Air Quality (PM2.5) Display, Ultra-Quiet 20dB Sleep Mode, HAP602 White
Levoit
LEVOIT Air Purifier for Home Allergies and Pets Hair Smokers in Bedroom, H13 True HEPA Filter, 24db Filtration System Cleaner Odor Eliminators, Remove 99.97% Dust Smoke Mold Pollen, Core 300, White
MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft², True HEPA Filter, B-D02L
Prices retrieved from Amazon on 2026-08-21 and may since have changed; the price on Amazon at the time of purchase is the one that applies. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. No manufacturer pays for a place in this list.
MERV 13 furnace filters
Affiliate linksMERV 13 is where a central-system filter starts capturing most fine particles including smoke. Check your blower tolerates the pressure drop first.
BNX
BNX TruFilter 20x20x1 Air Filter MERV 13 AC Filter, HVAC Furnace Filter, 6 Pack (ACTUAL SIZE 19.69"x19.69"x0.75") Allergies, Dust, Pet Dander & Smoke - MADE IN USA - MPR1500 / FPR 10
Aerostar
Aerostar Air Filter 16x25x1 MERV 13 AC Filter, HVAC, Furnace Filter, 6 Pack
BNX
BNX TruFilter 20x20x1 Air Filter MERV 13 AC Filter, HVAC Furnace Filter, 4 Pack (ACTUAL SIZE 19.68"x19.68"x0.75") Allergies, Dust, Pet Dander & Smoke - MADE IN USA - MPR1500 / FPR 10
BNX
BNX TruFilter 16x20x1 Air Filter MERV 13 AC Filter, HVAC Furnace Filter, 6 Pack (ACTUAL SIZE 15.69"x19.69"x0.75") Allergies, Dust, Pet Dander & Smoke - MADE IN USA - MPR1500 / FPR 10
Prices retrieved from Amazon on 2026-08-21 and may since have changed; the price on Amazon at the time of purchase is the one that applies. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. No manufacturer pays for a place in this list.
Questions
Filtration, answered
Does an air purifier remove radon?
No. Radon is a noble gas, not a particle, and it passes straight through a HEPA filter. No consumer air purifier meaningfully reduces radon in a home. The only thing that does is a mitigation system that stops the gas entering the building.
What MERV rating should I use in my furnace?
MERV 13 is the level at which a filter starts capturing most fine particles including smoke, and it is what the EPA and ASHRAE point to for improving indoor air. Check that your system can handle the pressure drop first: an undersized blower with a too-restrictive filter moves less air, which makes things worse rather than better.
How big a purifier do I need?
Match the CADR to the room. A rough rule from the AHAM guidance is that the smoke CADR in cubic feet per minute should be at least two thirds of the room's floor area in square feet. A 300 sq ft room therefore wants a smoke CADR of about 200 or more. Bigger is fine; you simply run it lower and quieter.
Are ionisers and ozone generators any good?
Avoid ozone generators entirely. Ozone is itself a lung irritant and a regulated pollutant, and California bans the sale of indoor air cleaners that emit ozone above a set limit. Ionisers and some plasma devices can produce ozone or reaction by-products as a side effect. Mechanical filtration is the technology with a straightforward evidence base.
How often do filters need changing?
Follow the manufacturer's interval, and shorten it during smoke season. A loaded filter restricts airflow, and a purifier working against a clogged filter delivers a fraction of its rated clean air. Replacement filters are the recurring cost that people forget when they compare purchase prices.
Next
Deal with the gas first
If your county is in a high radon zone, a mitigation system does more for the air in your house than any purifier will.