Quick answer
Choose a purifier sized for the room, compare its clean air delivery rate (CADR), check the exact filter claims, and price replacement filters before buying. Noise at the speed you will actually use matters as much as a headline maximum.
Size and CADR
CADR measures the volume of filtered air delivered for smoke, dust, and pollen, typically in cubic feet per minute in the US. Higher values can clean a larger room or do so more quickly. EPA suggests sizing by room area; its wildfire guidance recommends smoke CADR at least two-thirds of room area in square feet. This is a sizing rule, not a health guarantee. ACH means air changes per hour: an estimate of how often a room’s air volume passes through the cleaner, based on room volume and airflow. Ceiling height and chosen fan speed affect it.
| Your priority | Check |
|---|---|
| Bedroom | CADR at a quiet speed; room size and sleep mode noise |
| Large living room | Smoke CADR and stated area assumptions |
| Pets and dust | Particle filtration, pre-filter cleaning, replacement availability |
Filters and odor
A true HEPA filter is a defined high-efficiency particle filter; check the manufacturer’s exact claim and applicable test standard rather than treating “HEPA-type” as equivalent. Particle filters capture dust, pollen, and some pet dander; they do not remove gases by themselves. Activated carbon can adsorb some odors and gases, but effectiveness depends on the amount and type of carbon and the contaminant. Avoid blanket claims that a consumer purifier treats illness.
Noise, power, and cost
Compare sound ratings in decibels at the speeds you expect to use. Maximum CADR may be too loud for sleep, so look for low-speed airflow and independently measured sound where available. Check wattage, filter price, recommended replacement interval, and whether washable prefilters reduce routine upkeep. Actual filter life depends on air quality and use.
Choose by need
For a bedroom, prioritize quiet operation and a dimmable display. For wildfire smoke, consider smoke CADR and a well-sealed particle filter. For pets, plan to clean the prefilter frequently and choose adequate airflow. In rental rooms, a portable unit can complement ventilation, not replace source control.
Common mistakes
Do not size from a marketing area figure without checking its assumptions; compare CADR at comparable fan speeds. Do not expect a particle filter alone to remove cooking gases, or assume smart sensors prove better filtration. Product standards, plugs, voltage, units, and model names vary by country; verify the local model and replacement filters.
FAQ
What CADR do I need?
EPA’s rule of thumb for smoke is at least two-thirds of room area in square feet; use the maker’s room assumptions and consider higher airflow for more frequent cleaning.
Does HEPA remove odors?
No. HEPA targets particles; odor gases generally require an appropriate sorbent such as activated carbon.
How often should filters be replaced?
Follow the exact model manual. Dust load and operating hours change filter life.
Can an air purifier replace ventilation?
No. EPA recommends addressing pollution sources and ventilation alongside filtration.