Air Purifiers

Ignore the largest square-footage number on the box until you know how often that purifier cleans the room. A useful size decision starts with clean-air delivery, not maximum coverage marketing.

Measure length by width for square footage, then note whether the room has a standard ceiling. An open staircase, hallway, or double-height ceiling increases the air volume the purifier must handle. A purifier in a closed bedroom has a much easier job than the same unit beside an open kitchen and living area.

Place the purifier in the room where exposure or time spent is highest. Trying to clean an entire floor from one corner usually leads to poor air distribution, even when the total CADR looks adequate.

The EPA's practical sizing table uses a minimum smoke CADR around two-thirds of room square footage. A 300-square-foot room therefore starts around 200 cfm. This is a floor, not a reason to reject extra headroom.

Higher ceilings, fast smoke infiltration, severe allergies, or a desire to run quieter fan speeds justify moving up a size. More capacity lets the purifier meet the target without spending all day on its loudest setting.

What this means when shopping: Higher ceilings, fast smoke infiltration, severe allergies, or a desire to run quieter fan speeds justify moving up a size. More capacity lets the purifier meet the target without spending all day on its loudest setting.

The best location is close enough to the people or pollution source to matter, but open enough that the purifier can move air without fighting a wall, curtain, or sofa.

Check where your model pulls air in and where it sends clean air out. Keep those surfaces clear according to the manual. A round purifier still needs clearance if curtains collapse against its intake.

Do not hide the unit behind a sofa or push it under a desk because it looks cleaner. Restricted airflow reduces the amount of room air that reaches the filter and can raise fan noise.

In a bedroom, place the purifier where clean air can mix through the sleeping area without blowing directly into your face. In a living room, favor the seating zone rather than a distant hallway.

During wildfire smoke, a closed cleaner-air room is more controllable than an open central location. Move a portable unit if needed, but avoid carrying a loaded filter roughly or operating it on an unstable surface.

What this means when shopping: During wildfire smoke, a closed cleaner-air room is more controllable than an open central location. Move a portable unit if needed, but avoid carrying a loaded filter roughly or operating it on an unstable surface.

A filter timer is an estimate of hours, not a microscope. Smoke load, pets, remodeling dust, fan speed, humidity, and hours of use can move the real replacement date in either direction.

Washable or vacuumable prefilters catch hair and coarse dust. Clean them according to the manual so the fan does not have to pull through a blanket of debris.

Most pleated particle filters should not be washed. Water can damage the media and its seal. If the manual says replace, replace rather than trying to make a disposable filter look new.

A reset light usually counts run time. Check the filter for dark loading, persistent odor, falling airflow, or a fan that sounds strained. A filter can discolor normally without being finished, so use several clues together.

During wildfire season, inspect more often. A purifier that ran continuously through dense smoke may use a meaningful part of its filter life in weeks.

What this means when shopping: During wildfire season, inspect more often. A purifier that ran continuously through dense smoke may use a meaningful part of its filter life in weeks.

Clean Air Delivery Rate combines airflow and particle-removal efficiency into one useful number. It is not every aspect of purifier quality, but it is the clearest place to start.

CADR is reported in cubic feet per minute. Smoke CADR reflects the purifier's delivery of air cleaned of smaller smoke particles, while dust and pollen figures use different test aerosols.

Smoke CADR is commonly used for sizing because fine-particle control is a central reason to own a purifier. Compare models at their maximum rated setting, then leave noise headroom for everyday use.

A fan can move a large volume of air that is not fully cleaned. CADR accounts for both flow and removal efficiency, which makes it more informative than an unlabeled CFM claim.

The number still comes from controlled testing. Room geometry, open doors, a clogged filter, and reduced fan speed change results at home.

What this means when shopping: The number still comes from controlled testing. Room geometry, open doors, a clogged filter, and reduced fan speed change results at home.