How to Choose an Air Purifier

This page is the method this whole site runs on, written as a sequence you can follow in a shop. It is deliberately boring, and following it will stop you buying the two most common wrong machines: the one that is too small for the room, and the one that costs three times as much to run as its neighbor on the shelf.

Length times width in feet. If the ceiling is higher than eight feet, note that too, because AHAM’s published room sizes assume eight and a ten-foot ceiling is 25% more air in the same footprint.

This is where most of the money in this category is lost, and it is lost before anyone reads a specification. Coverage claims on boxes routinely run about 4.8 times the certified figure, because the claim is computed at one air change per hour and the certification is computed at 4.8. A machine advertised for 1,718 square feet is certified for 358.

AHAM’s own rule: the CADR should be at least two-thirds of the room’s floor area in square feet, at a 8-foot ceiling. It is one multiplication.

The size calculator does this with your actual dimensions including ceiling height, and takes about ten seconds.

Two public databases matter. AHAM’s VERIFIDE directory lists models independently verified to ANSI/AHAM AC-1. EPA’s ENERGY STAR room air cleaner database requires testing to the same standard through an EPA-recognized certification body, and additionally publishes measured ozone emissions and certified annual energy use.

Search the model number in both. Three outcomes: it is in one, it is in both, or it is in neither. In neither is not a disqualification — some capable machines are not listed, including the single most-recommended purifier in this category — but it means the numbers you are comparing came from the company selling the machine. Every model we cover, with its register is a shortcut for the machines on this site.

Many air cleaners include an ion generator, a plasma stage, an electrostatic precipitator or a UV lamp. EPA’s position is direct: avoid portable air cleaners that intentionally produce ozone, because ozone is a lung irritant.

ENERGY STAR publishes a measured ozone emission in parts per billion for every certified unit. Across the machines we cover those readings run from 0.00 to 5 ppb against a 50 ppb program limit — so all of them are legal, and there is still a real difference between a measured zero and a measured five. If the machine is for a bedroom occupied by somebody with asthma, that difference is the one we would spend on.

Certified annual energy use is published per model and it is the number that decides the long-run bill, because a purifier that helps is a purifier that runs continuously. Across the units on this site it spans 39 to 657 kWh a year and it correlates poorly with output.

The cleanest example: Winix’s own 5500-2 uses 31% more electricity a year than the same company’s AT41 and delivers less certified air. Same brand, same era, opposite value. What an air purifier actually costs to run does the arithmetic at a named electricity rate.

Filters are the other half of the bill and the half nobody prices at the point of purchase. A cheap machine on an expensive filter platform is not cheap. Where a manufacturer publishes an interval and a price we print both; where they do not, we print “Not published” rather than an estimate, and you should treat that absence as information — filter cost over three years changes rankings.

A real living room, 20 feet by 15, with a nine-foot ceiling and a cat. Here is the sequence end to end, with the arithmetic shown rather than asserted.

Step 1, measure. 20 x 15 is 300 square feet. The ceiling is nine feet rather than the 8 AHAM assumes, which is 12.5% more air in the same footprint — so treat it as a slightly larger room than the floor area suggests.

Step 2, convert. AHAM’s two-thirds rule asks for 200 CFM at eight feet. Correcting for the ninth foot puts the real requirement nearer 226 CFM. That single correction is the difference between two very different shortlists, and almost nobody makes it.

Step 3, check the register. Searching the shortlist in AHAM’s directory and the ENERGY STAR database at that figure removes most of the shelf immediately. The Honeywell HPA6000 comes back at 257 certified CFM — comfortably over. The Coway AP-1512HH, which is what most people in this situation buy, comes back in neither register.

Step 4, check ozone. The HPA6000 measures 0.00 ppb and is classified fan-and-filter. The Blueair 311i Max, which is more efficient and also clears the requirement, measures 2 ppb and carries an ion stage that is not documented as switchable. With a cat in the house and nobody asthmatic, that is a live trade; with somebody asthmatic it is not.

Step 5, check running cost. $38 a year for the Honeywell against $35 for the Blueair. Both are cheap. The machine that would have cost $120 a year for less certified air is the one this step exists to catch.

Step 6, check filters. Neither manufacturer publishes a filter price we could source for these two, so the honest position is that this step returns “unknown” for both — and knowing that before you buy is still better than discovering it at the first replacement.

Total time: a few minutes. What it prevents is the two failures that dominate this category — a machine sized for the box’s coverage claim rather than the room, and a machine whose electricity bill quietly exceeds its purchase price over its life.

One at each of the sizes most people are buying for. All three are in a certification register, all three have a published measured ozone figure, and all three are current products we could confirm at retail.

Electricity costs on this page use 18.34¢ per kWh, the U.S. average residential price for June 2026 from the U.S. Energy Information Administration, Electric Power Monthly, Table 5.3. Your rate is on your bill and is probably not this one; multiply the kWh figure by your own rate and you have your number.

• “True HEPA” on the box. It is a marketing phrase with no certifying body in the consumer market, and the registers frequently classify those same filters HEPA-Type.
• “Captures particles as small as 0.003 microns”. Filtration efficiency has a minimum around 0.3 microns and improves on both sides of it, so this describes an easier job while implying a harder one.
• Coverage claims without an air-change rate attached. A square footage with no ACH figure next to it is not a specification.
• Star ratings and review counts. We do not use them and neither should you for this decision; they measure satisfaction with delivery and looks at least as much as they measure clean air.

If you would rather skip the method and read a ranking, the flagship allergy roundup applies all six checks for you, and how we pick sets out where the method runs out.