Air Purifiers and HEPA Filters and What the EPA Says About CADR and Ozone (2026 Buying Guide)
Last updated: October 22, 2026.
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- Choose a portable air cleaner with a CADR large enough for your room (for example, at least 130 cfm for a 200 square foot room, per the EPA).
- Avoid air cleaners that intentionally produce ozone, a lung irritant (EPA).
- Replace filters on the manufacturer’s schedule, typically every 60 to 90 days.
- Popular air purifiers and monitors are listed below with Amazon links. The EPA does not recommend specific brands.
Air purifiers are popular, but the market is full of confusing claims. Some devices filter particles well. Others add little, and some intentionally produce ozone, a lung irritant. This guide summarizes the U.S. Environmental Protection Agency’s (EPA) Guide to Air Cleaners in the Home and related guidance from the California Air Resources Board (CARB), and lists popular, widely reviewed air purifiers on Amazon. The EPA says it does not certify or recommend specific brands or models, so use this as a checklist, not an endorsement.
1. Why Indoor Air Matters
The EPA says indoor air contains pollutants that can affect human health, from outdoor sources and from indoor sources and activities such as cooking, cleaning, secondhand smoke, building materials and consumer products. Common indoor contaminants include fine and coarse particulate matter (PM2.5 and PM10), formaldehyde, mold and pollen. Since most people spend about 90% of their time indoors, much of their exposure to airborne pollutants happens in their homes.
2. How to Choose a Portable Air Cleaner (EPA)
- Match the CADR to your room. To filter particles, choose an air cleaner with a clean air delivery rate (CADR) large enough for the size of the room. The higher the CADR, the more particles it can filter and the larger the area it can serve. Most packaging tells you the largest room size. The EPA gives a rough guide for an 8-foot ceiling: a 100 square foot room needs a minimum CADR of 65 cfm, 200 sq ft needs 130, 300 sq ft needs 195, 400 sq ft needs 260, 500 sq ft needs 325 and 600 sq ft needs 390.
- HEPA filters. Portable air cleaners often achieve a high CADR by using a high-efficiency particulate air (HEPA) filter.
- For gases and odors, choose one with an activated carbon filter or another filter designed to remove gases. The EPA notes there are no widely used performance rating systems for gas removal.
- Avoid ozone. The EPA says to avoid portable air cleaners and furnace or HVAC filters that intentionally produce ozone, a lung irritant.
- Replace filters according to the manufacturer. The EPA notes that manufacturers typically recommend replacement every 60 to 90 days, and that heavily soiled filters should be changed more often.
3. Beware of Ozone
The EPA says ozone generators that are sold as air cleaners intentionally produce ozone, and no federal government agency has approved these devices for use in occupied spaces. It adds that air cleaners that contain electrostatic precipitators, ionizers, UV lights without adequate lamp coatings, and plasma air cleaners may have the potential to emit ozone. Both CARB and the Association of Home Appliance Manufacturers (AHAM) maintain lists of air cleaners tested and shown to emit little or no ozone. Since 2010, all portable indoor air cleaners sold in California must be CARB-certified, with an ozone limit of 0.050 parts per million. CARB notes that certification does not reflect how effective a cleaner is.
4. What an Air Cleaner Can and Cannot Do
The EPA says several studies using portable HEPA air cleaners have found small improvements in cardiovascular and respiratory health, and that portable air cleaners may reduce allergy or asthma symptoms, though the improvements are typically small and not always noticeable. It also says no air cleaner or filter will eliminate all of the pollutants in your home, and they will not solve a mold and moisture problem. For a central furnace or HVAC system, the EPA suggests a filter rated at least MERV 13, or as high as your system will accommodate. Source control and ventilation still matter.
5. Popular Air Purifiers on Amazon
These are widely reviewed examples. Read the product page for the room size, CADR and filter type, and confirm the device does not use an ionizer or produce ozone if you want to avoid ozone. The listings do not guarantee any particular certification.
| Product | What stands out |
|---|---|
| Levoit Air Purifier for Home, Pets, Hair and Allergens in Bedroom | Quiet, bedroom-size purifier |
| PuroAir 240 HEPA Air Purifier | HEPA, large room rating on the listing |
See Levoit Air Purifier on Amazon →
As an Amazon Associate I earn from qualifying purchases.
See PuroAir 240 on Amazon →
As an Amazon Associate I earn from qualifying purchases.
Browse replacement HEPA filters on Amazon →
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6. Air Quality Monitors (Optional)
A small monitor can show PM2.5, temperature and humidity so you can see when your air is worse, for example while cooking. Keep in mind that consumer monitors vary in accuracy.
For alarms that protect against fire and carbon monoxide, see our guide to smoke and carbon monoxide alarms. For flu season habits, see our flu season guide.
7. Frequently Asked Questions
What does CADR mean?
Clean air delivery rate. The EPA says it measures how much filtered air a purifier delivers, and a higher CADR means it can filter more particles and serve a larger area.
Are ozone air purifiers safe?
The EPA says to avoid air cleaners that intentionally produce ozone, a lung irritant, and that no federal agency has approved ozone generators for use in occupied spaces.
How often should I change the filter?
Follow the manufacturer. The EPA says they typically recommend every 60 to 90 days, and that soiled filters may need earlier replacement.
Will an air purifier fix mold?
No. The EPA says air cleaners will not resolve a mold and moisture problem. They may remove some of the particles mold generates.
Is this professional advice?
No. This is general information. Ask your doctor about asthma, allergies or lung conditions.
Sources
- EPA: Guide to Air Cleaners in the Home
- EPA: What are ionizers and other ozone generating air cleaners?
- CARB: List of CARB-Certified Air Cleaning Devices
As an Amazon Associate I earn from qualifying purchases. This guide is general information, not medical or professional advice. This site is not affiliated with any government agency or product maker.
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