HEPA cleaners

HEPA air cleaners are useful when:

• You are supplementing an existing HVAC system.
• There is no HVAC system.
• Outside air pollution is high (such as during wildfire smoke events).
• There are crowded spaces.
• There is a respiratory disease outbreak.
• You or a family member have a specific medical condition, such as asthma or allergies.

What kind of HEPA air cleaner to look for

• Use HEPA or True HEPA filters, meaning they are at least 99.97% effective at filtering particles as small as 0.3 microns.
• Are verified by AHAM to have a clean air delivery rate (CADR) adequate for the size of the space. Higher CADRs (above 200 cfm) are more efficient and better for larger spaces. The unit should have a room size and CADR indicated in its specifications. Generally, you want a CADR of 65 for every 100 square feet of room space (so 130 for a 200 square foot room, 195 for a 300 square foot room, etc.)
• Usually, the CADR listed is for the unit's highest fan speed. If you use a lower fan speed, or the "auto" setting, you likely will not get the full CADR listed, and may need multiple units to achieve the right CADR for your room.
• Do not have additional technologies or features (e.g., ionization, UV lights, and oil diffusers) because they can cause unintended health hazards, unless they are third-party verified (see last point below).
• Have a filter replacement schedule that will be easy to follow based on the manufacturer's recommendations.
• Are quiet. Look for a noise rating of 50 decibels (dB) or less (roughly the operating noise of a refrigerator). If you have a quiet space you need to maintain, you can buy a bigger HEPA air cleaner than you’d normally need so it can run at a lower fan speed to reduce noise.
• Have third-party verification of filter efficiency, energy star and low-ozone certification through the Association of Home Appliance Manufacturers (AHAM) searchable list of portable air cleaners certification and the California Air Resources Board (CARB) list of low ozone emitting units.

How many HEPA air cleaners you need for your space

Having more than one unit in a room may be necessary for adequate filtration.

To know how many units you need:

1. Estimate the CADR (filtration rate) for your room size using EPA's Guide to Air Cleaners in the Home. Generally, you want a CADR of 65 for every 100 square feet of room space (so 130 for a 200 square foot room, 195 for a 300 square foot room, etc.)
1. The numbers provided assume an 8-foot ceiling height. If a space has a higher ceiling, the resources provided below can help you calculate the needed CADR based on the volume of your room. The numbers above also provide 4-5 air changes per hour (ACH) in the specified room size (5 is the minimum the CDC recommends). If you have an HVAC system, or other ventilation that provides a certain number of ACH, you may not need a full 4-5 ACH from a HEPA air cleaner.
2. Purchase HEPA air cleaners that, when added, create the minimum CADR needed. Multiple units may be placed in the same space to achieve the recommended CADR.
1. For example, if your room area (length x width) is 500 square feet with an 8-foot ceiling, you can get one HEPA air cleaner that has a CADR of 325 or higher, or two HEPA air cleaners that have a CADR of 175 each, adding up to a CADR of 350.
3. Choose a unit with a higher CADR than needed for the space. This allows you to get enough filtration even on lower, quieter settings that may be used in classrooms or sleeping areas.

How to use a HEPA air cleaner

• Keep it on higher fan speeds to filter more air.
• Leave the HEPA air cleaner on. It is not effective when turned off.
• Place in areas where people spend the most time.
• Place the cleaner in an area that will avoid blowing air from one person onto another.
• Do not place air cleaners where walls, furniture, curtains, or other objects will block the unit’s air intake and outlet.
• Most units plug into electrical outlets. Secure cords to avoid tripping hazards.
• Always follow manufacturer safety recommendations to protect children from any possible hazards posed by the air cleaner.
• Reduce indoor air pollution by, for example, establishing a no-smoking perimeter around doorways and windows of the building and installing functional cooking fume hood/exhaust fans in kitchen, bathroom, and laundry areas.
• Note: When pollution is high outdoors (such as during a wildfire episode), close windows and doors while the air cleaner is on.