Graham FisherBy Graham Fisher

Updated November 2026

An air purifier helps with airborne particles and some odors. A unit with a true HEPA filter captures dust, pollen, pet dander, dust mite debris, smoke particles and many mold spores that float through a room. Activated carbon layers can reduce certain gases and smells, such as cooking odors, pet smells and some smoke. It does not clean surfaces, remove mold growing on walls, or fix the source of a problem.

Why Air Purifiers Work on Some Problems and Not Others

An air purifier pulls room air through a filter, so it can only treat what is suspended in the air. Dust, pollen and pet dander are small enough to drift and get caught in the filter media. Gases and odors are different. They pass through a HEPA filter unless the unit also has activated carbon, and even then the carbon only holds a limited amount before it saturates.

Shopping for one? See our guide: What Is Better for Allergies Humidifier or Air Purifier (2026): Which Should You Choose?.

Anything settled on a floor, couch or bed stays put until you vacuum or wipe it. The purifier will eventually pick up some of that material as it gets stirred up, but it will not do the job of cleaning surfaces.

Factors That Decide How Well It Performs

Three things matter most. First, the clean air delivery rate (CADR), which manufacturers list for smoke, dust and pollen. A higher number means the unit moves more clean air per minute. Second, room size: a unit rated for a 300-square-foot room will be underpowered in a 600-square-foot open plan. Third, filter type. Look for a true HEPA filter rather than a “HEPA-like” or “HEPA-type” label, and check whether the unit includes activated carbon if odors are your concern.

Runtime matters too. A purifier on a low fan setting may run quietly all day but clean less air per hour than on medium or high. Many owners run the unit on a higher setting for a short period after cooking, vacuuming or a smoky event, then drop to a lower setting.

What to Do Next

  1. Match the unit to your room size using its CADR rating. Choose a model rated for a space larger than the room you plan to use it in.
  2. Place it near where you spend the most time, with clear space around the intake and outlet. Keep it away from walls and curtains.
  3. Keep doors and windows closed while it runs so it can keep up with incoming air.
  4. Replace or clean filters on the schedule the manufacturer gives. A clogged filter reduces airflow and performance.
  5. Address the source. Fix leaks, reduce humidity, clean litter boxes and vacuum regularly with a HEPA-rated vacuum. An air purifier works best alongside these steps.

What We’d Use

For a general-purpose room, a true HEPA unit with a moderate CADR is a sensible starting point, such as the Levoit Core 300. View on Amazon

If odors are the main concern, look for a model that combines HEPA with a thick activated carbon layer, such as the Winix 5500-2. View on Amazon

FAQ

Will an air purifier remove mold from my walls?

No. A purifier can capture some mold spores floating in the air, but it does not kill or remove mold growing on surfaces. Mold growth needs to be cleaned or repaired at the source. For larger problems, consult a professional remediation company.

Does an air purifier help with allergies?

It can reduce airborne triggers such as pollen, dust and pet dander in the room where it runs. Results vary by person and by trigger. If you have significant allergies or asthma, consult an allergist or doctor before relying on a purifier as part of your plan.

How long does it take to clean the air in a room?

It depends on the unit’s CADR and the room size. Manufacturers often give an estimate of how long it takes to cycle the room’s air, and many people run their unit for several hours a day to maintain cleaner air.

Ready to choose one?

Graham Fisher

About Graham Fisher

Graham Fisher is part of our editorial team and reviews and edits our indoor air guides, checking product details against manufacturer specifications and owner feedback.