Every air purifier gets a score from 0 to 100% built from six factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Purifiers are ranked within their size, set by certified smoke CADR: small rooms (under 150 cfm), medium rooms (150 to 249) and large rooms (250 and up).
| Factor | Measures | Weight |
|---|---|---|
| Value | price per cfm of clean air | 25% |
| Filter cost | yearly filter cost for the air it cleans | 20% |
| Quiet | sound at top speed | 20% |
| Efficiency | clean air per watt | 15% |
| Auto mode | air-quality sensor and app | 10% |
| Warranty | warranty length | 10% |
Where the numbers come from
CADR (clean air delivery rate) is measured under the AHAM AC-1 standard: how many cubic feet per minute of smoke, dust and pollen-free air the purifier delivers at top speed. We take it from the AHAM Verifide directory, where an independent lab tests each model, or from the ENERGY STAR certified room air cleaner list. A few makers publish an AC-1 figure for models in neither list; those are marked on the product page as maker-rated. We size and rank on smoke CADR because smoke particles are the smallest and hardest to catch.
The room size shown is AHAM’s: 1.55 times the smoke CADR, for a room with an 8-foot ceiling. It assumes the air is filtered about five times an hour. Makers’ own coverage figures are often far larger because they assume once an hour, and they aren’t used.
Noise, filter price and life, sensors and warranty come from the maker’s spec sheet, manual or store. Filter prices are checked on the same date as the purifier’s price.
The factors
Value is the price divided by smoke CADR: dollars per cfm of clean air. Small purifiers cost more per cfm, so each size has its own scale:
| Size | Scores 0 | Full marks |
|---|---|---|
| Small rooms | $2.00 per cfm | $0.50 per cfm |
| Medium rooms | $1.80 per cfm | $0.50 per cfm |
| Large rooms | $1.60 per cfm | $0.45 per cfm |
Filter cost is the price of a genuine replacement filter set times the number of replacements a year at the maker’s stated interval, divided by smoke CADR. $80 a year per 100 cfm scores zero and $10 full marks. Filters often cost more over a purifier’s life than the purifier itself, so this carries nearly as much weight as price. Running a purifier less than all day stretches the interval, but the comparison between models holds.
Quiet is the maker’s sound rating at top speed, where the CADR is measured: 60 dB(A) scores zero and 45 dB(A) full marks. Most purifiers spend most of their time on a lower speed and are much quieter there; the low-speed figure is shown on each product page. Makers measure at different distances, so treat it as a guide.
Efficiency is the integrated energy factor: certified smoke CADR per watt, including standby power. 2 cfm per watt scores zero and 10 full marks. A purifier that runs all day typically uses 100 to 400 kWh a year, so efficiency adds up.
Auto mode: an air-quality sensor that speeds the fan up when it detects smoke or dust scores 70% of the factor, and a Wi-Fi app the other 30%. A sensor matters more than an app because it raises the fan when you need it and lowers it, saving filter life and noise, when you don’t.
Warranty: 1 year scores zero and 5 years full marks.
What isn’t scored
Ionizers and ozone. Some purifiers add an ionizer or “plasma” stage. It can create small amounts of ozone, a lung irritant. Every purifier sold in California must be certified by CARB to emit very little ozone, and each product page says whether the unit has an ionizer, whether it can be switched off, and whether it’s on CARB’s list. A purifier’s filter does the work either way, so it isn’t scored.
Coverage claims, filter type labels (“True HEPA”, “H13”), activated carbon, fan speeds and weight are listed but not scored: CADR already measures how well the filter works as installed. Independent tests are listed where they exist, but there are too few to score.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each size. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.