Buying & Equipment · buying guide
The Air Purifier Buying Checklist
ending with the only figure comparable between brands
Work down the list. Do not start at the checkout.
Most bad air purifier purchases are not bad luck, they skipped a checkable step. This page is the checklist, in the order that catches problems cheapest: the room first, the numbers second, the feel-good features last.
Six checks, then a short section on each. None of them require trusting a box.
The six checks, in order#
- 1Measure the room. Length times width, in feet.
- 2Read the published minimum CADR for that area, and round up between sizes.
- 3Check the tobacco-smoke CADR, not just the headline number.
- 4Ceiling above eight feet? Aim higher than the minimum.
- 5Check filter availability and the lifetime cost of owning the unit.
- 6Check noise at the speed you will actually run.
Checks 1 and 2: measure the room, read the published minimum#
EPA publishes a minimum clean air delivery rate for each room area, calculated on an eight-foot ceiling. The table is published in 100 sq ft steps and stops at 600 sq ft:
| Room area (sq ft) | Minimum CADR (cfm) |
|---|---|
| 100 | 65 |
| 200 | 130 |
| 300 | 195 |
| 400 | 260 |
| 500 | 325 |
| 600 | 390 |
Check 3: the tobacco-smoke CADR#
The standard test produces three CADR figures, dust, pollen and tobacco smoke. Smoke is the smallest test particle, so the smoke CADR is the one that exposes a weak unit.
EPA's guidance is direct: to remove small particles, choose a portable air cleaner with a high CADR for tobacco smoke. The third check is making sure that number exists, is printed, and clears the minimum for your room: compare HEPA air purifiers on their published CADR.
Suggested next step
Compare what the table asks for
Search listings for the published minimum your room needs, then check the smoke CADR on the shortlist before anything else.
Check 4: ceilings above eight feet#
EPA's minimums are calculated on an eight-foot ceiling. A taller room holds more air than its floor area suggests, and the table's row quietly assumes you know that.
If your ceiling is above eight feet, treat the row as a floor and aim higher. The honest adjustments are judgment calls from here, but they are your judgment, informed by a published number.
Checks 5 and 6: filters, lifetime cost, and noise at your speed#
The unit is bought once; the filters are bought for as long as you own it, on a cadence only the maker sets. Check replacement availability before purchase, a purifier whose filters are scarce is a decision you make repeatedly and get to make only once.
Noise is speed-specific: the published figures that matter are for the speed the unit runs at to meet your room's minimum, not the showroom whisper. A unit with CADR headroom runs slower and quieter for the same delivery. That is the whole trick, and it is check 2 wearing headphones.
Questions people actually ask
Sources
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30
Quoted and transcribed, never paraphrased into new numbers. This site does not interpolate between published figures.
Suggested next step
One more angle before you decide
The minimum is settled, spend the rest of the decision on noise, filter cost and the smoke CADR.
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Printed from https://roomandfilter.com/equipment/air-purifier-buying-checklist, “The Air Purifier Buying Checklist”. Figures from U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30. No prices are shown on this site, by policy.