Do Air Purifiers Help With Viruses? What the EPA and CDC Say
Do air purifiers help with viruses like flu and COVID? What the EPA, CDC and ASHRAE say about HEPA, air changes per hour, ventilation, and technologies to avoid.
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Yes, within limits. Respiratory viruses travel on airborne particles, and a HEPA air purifier sized for the room removes those particles, which the EPA says can help reduce airborne contaminants including viruses. But the EPA is equally clear that air cleaning or filtration by itself is not enough to protect people, and that it is not a substitute for ventilation or other measures. The CDC's NIOSH guidance suggests aiming for five or more air changes an hour of clean air in occupied rooms, and portable purifiers count toward that.
No air purifier is proven to prevent illness, and none should be marketed as if it does. What a purifier can do is lower the amount of virus-carrying aerosol in a room, which is why it is most useful where someone is sick or many people share a space.
How purifiers affect airborne viruses
When people breathe, talk, cough or sneeze, they release respiratory particles of many sizes. The smaller ones can stay airborne for minutes to hours and build up in rooms with poor ventilation. A HEPA filter captures particles across that range, so a purifier with enough clean air delivery rate (CADR) reduces how many build up. It does nothing for droplets that travel straight from one person to another at close range, or for surfaces.
What the agencies recommend
| Source | What it says |
|---|---|
| EPA, Air Cleaners, HVAC Filters, and Respiratory Viruses | Air cleaners and HVAC filters can help reduce airborne viruses; not enough on their own; use MERV 13 or higher in HVAC where the system allows; portable cleaners should be sized for the room and be HEPA, smoke-CADR rated, or remove most particles under 1 micron; do not use ozone generators in occupied spaces |
| CDC/NIOSH, Aim for 5 | Aim for 5 or more air changes an hour of clean air, a rough benchmark; filtration and air cleaners count as equivalent air changes |
| ASHRAE, Standard 241 | Sets equivalent clean airflow targets per occupant, met by ventilation, filtration and air cleaning together; filters at least MERV 11 |
How to size a purifier for a sick room
Use the CDC's five air changes an hour as the floor. Room volume (length x width x ceiling height) x 5 / 60 gives the smoke CADR you need. Smoke CADR is the right figure here because it covers the smallest particles.
| Room | Floor area | Smoke CADR | Example AHAM-listed pick |
|---|---|---|---|
| Small bedroom | 120 sq ft | 80 cfm | Levoit Core 200S-P (90 cfm) |
| Bedroom | 200 sq ft | 133 cfm | Levoit Core 300-P (143 cfm) |
| Living room | 320 sq ft | 213 cfm | Levoit Core 400S-P (231 to 234 cfm) |
| Classroom-size room | 700 sq ft | 467 cfm | Two purifiers, or a large unit plus ventilation |
Our sizing calculator does the sum for your room.
Where to put it
The EPA suggests placing portable air cleaners where people spend the most time, or near a vulnerable person or someone who is isolating, and directing airflow so it does not blow from one person directly toward another. In a sick room, put the purifier near the patient with the outlet aimed into the room, and keep the door closed.
Ventilation still comes first
Opening windows, running bathroom and kitchen exhaust fans, and running the HVAC fan with a good filter all bring in or clean air. The EPA describes portable air cleaners as a supplement to ventilation and HVAC filtration, especially where ventilation is hard to improve, not a replacement. A CO2 monitor gives a rough idea of how well a room is ventilated; see our CO2 guide.
Technologies to be careful with
- Ozone generators. The EPA says not to use them in occupied spaces; at concentrations within health limits, ozone does not effectively remove viruses.
- Bipolar ionization. The EPA calls it an emerging technology with little research outside the lab and warns of possible ozone and byproducts; if used, choose UL 2998 devices. See our ionizer guide.
- "Kills 99.9% of viruses" claims. These usually come from small test chambers, not real rooms, and often from the maker's own testing.
- UV lamps in portable purifiers. Air passes the lamp too quickly for much exposure in many designs; the filter does the measurable work.
What to buy
A plain HEPA purifier with a certified smoke CADR that gives the room five or more air changes an hour. In our best air purifiers list, the Levoit Core 300-P suits a sick room and the Levoit Core 400S-P a living room. For a whole house, add a MERV 13 furnace filter if your system can take it; see our MERV 13 guide.
Frequently asked questions
Do air purifiers remove viruses from the air?
HEPA purifiers remove airborne particles that carry viruses, and the EPA says air cleaners can help reduce airborne viruses. They do not stop close-range spread or surface contamination, and the EPA says air cleaning alone is not enough to protect people.
Can an air purifier help with COVID or flu?
It can reduce virus-carrying particles in a room, which is most useful where someone is sick. It does not prevent illness and is a supplement to ventilation, vaccination and other measures.
How many air changes per hour help reduce viruses?
The CDC's NIOSH guidance suggests aiming for five or more air changes an hour of clean air, a rough benchmark. Portable air cleaners count toward that total.
Is a HEPA filter enough to catch viruses?
HEPA filters capture particles across the size range that carries respiratory viruses. What limits a purifier is usually its CADR relative to the room, not the filter.
Do UV air purifiers kill viruses?
UV can inactivate microbes with enough exposure, but in many portable purifiers air passes the lamp too quickly for much effect. The HEPA filter does the measurable work.
Where should I put an air purifier in a sick room?
Near the sick person with the outlet aimed into the room and the door closed, and avoid blowing air from one person directly at another, as the EPA advises.
Sources
- Air Cleaners, HVAC Filters, and Respiratory Viruses, US Environmental Protection Agency
- How Much Ventilation Is Enough? Aim for 5, CDC, National Institute for Occupational Safety and Health
- ASHRAE Publishes Standard 241, Control of Infectious Aerosols, ASHRAE
- Guide to Air Cleaners in the Home, US Environmental Protection Agency
- AHAM Verifide Directory: Certified Room Air Cleaners, Association of Home Appliance Manufacturers
Related guides
Air Purifiers and Ozone: Which Ones Emit It and How to Check
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CADR Explained: What Clean Air Delivery Rate Measures and Why It Matters
CADR is the one standardized number for how fast an air purifier cleans a room. Here is how it is measured, how to use it, why smoke CADR is the one to compare, and its blind spots.
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