Best Air Purifier by Room Size (and What Each Costs a Year)

Multiply the room's square feet by two thirds for the minimum smoke CADR at an 8 ft ceiling. 150 sq ft needs 100 cfm, 300 sq ft needs 200, 500 sq ft needs 334. Add about 25 percent for allergies, pets or smoke.

Per year, the Winix A230 at about $101 including its one filter. For large rooms, the Blueair Blue Pure 211i Max at about $160, because it draws 44 W on high for 435 cfm.

Yes. A bigger unit reaches the same air cleaning on a lower fan speed, which is quieter and often uses less power. Unlike an air conditioner, there is no penalty for oversizing beyond the price.

They usually assume fewer air changes per hour than AHAM's rule. Compare the AHAM room size or the smoke CADR on the label instead.

Watts x 24 hours x 365 days / 1,000 = kWh a year, times your rate. On high around the clock at 17.3 cents per kWh, the 44 W Blueair Blue Pure 211i Max uses about 385 kWh, or $67 a year, and the 109 W Honeywell HPA5300B uses about 955 kWh, or $165. Lower fan speeds draw much less, so these are the upper end.

Follow the maker's interval: about every 6 months for the Levoit Core 300, Core 400S and Core 600S, about every 9 months for the Blueair Blue Pure 211i Max, and once a year for the Winix A230, Winix 5520, Coway AP-1512HH and Honeywell HPA5300B. Heavy smoke, pets or round-the-clock use on high can mean replacing sooner.

Yes, for steady results, because a purifier only cleans the air while it runs. During wildfire smoke, EPA advises running it as much as possible on the highest fan setting you can tolerate. Auto mode, on models like the Coway AP-1512HH, turns the fan down when the air is clean to save power and noise.

CADR is the Clean Air Delivery Rate, the cubic feet per minute of filtered air a purifier delivers, measured under AHAM's test for smoke, dust and pollen. Smoke particles are the smallest and hardest to catch, so smoke CADR is the number to size by. For example, the Winix 5520 is rated 253 cfm for smoke, 252 for dust and 247 for pollen.

At least 267 cfm of smoke CADR by AHAM's two-thirds rule, or about 334 cfm with 25 percent extra for allergies or pets. The Honeywell HPA5300B (323 cfm) meets the minimum, and the Coway Airmega 350 (360), Levoit Core 600S (391) and Blueair Blue Pure 211i Max (435) clear the sized-up target.

Usually, because ENERGY STAR sets a minimum smoke CADR per watt. Divide smoke CADR by watts on high to compare: the ENERGY STAR Blueair Blue Pure 211i Max delivers about 9.9 cfm per watt (435 / 44), while the Honeywell HPA5300B delivers about 3.0 (323 / 109). At the same airflow, the higher number means a smaller power bill.