HEPA Filters


The campus response to the Coronavirus pandemic includes a combination of protective measures with vaccination and masking being the most important. 

The use of high-efficiency purified air (HEPA) cleaners has been suggested by agencies like the California Department of Public Health (CDPH) and the Centers for Disease Control (CDC) for improving ventilation indoors when there is insufficient fresh air introduced by HVAC systems, or natural ventilation from windows.

While the use of HEPA air cleaning devices may reduce the presence of airborne viral particles in a room, their use should be carefully considered before using.


Facilities Services has increased the percentage of outdoor air in campus buildings where feasible, per CDC and CDPH guidance, as part of the multi-layer strategy to limit the spread of Coronavirus. There remain buildings without mechanical ventilation that rely on windows for fresh air that should be opened when spaces are occupied.  


The campus has generally assessed whether the use of portable or mounted High Efficiency Particulate Air (HEPA) filtration units, or other air cleaning systems, would reduce the risk of COVID-19 transmission and concluded that in some cases they should not be used because of the following: 

  • Air currents that can spread untreated air to other people in the space

  • Noise that increases with the fan speed

  • Maintenance and filter replacement considerations

  • Energy consumption and potential power failures

  • Theft of unattended devices

If you are interested in using filtration units, please contact EH&S at 510-642-3073 or EHS@berkeley.edu(link sends e-mail) to assess if using HEPA air cleaners in your location would be helpful.  Please also contact Facilities Services at 2-1032 to submit a work order to confirm that your area has sufficient electrical capacity if several HEPA filtration units are to be considered.

  • Portable HEPA filtration units must be approved for use in California (look for the label CARB-compliant; this means they are tested for electrical safety and ozone emissions). 
  • Ensure the unit is sized appropriately for the intended space. Some large classrooms may require more than one unit. One method for selecting the appropriate size unit is checking that the Clean Air Delivery Rate (CADR) is at least 2/3 of the room's floor area (in square feet), with adjustments made for high ceilings. A list of units with CADR ratings can be found on AHAM's "Verifide" website.
  • For classroom use, look for quieter models with a noise level < 50 dBA if possible.

In all cases, it is recommended that each use of a HEPA air cleaner be thoughtfully reviewed before purchase.  Remember that ventilation is only one part of many strategies that limit the spread of Coronavirus.  Weigh the above considerations before contacting EH&S to determine whether a HEPA filter could be an option.  


Although fans can increase ventilation if installed where they bring in outside air, fan use is not recommended anywhere multiple people may be present in an indoor environment. A fan blowing across a sick person can increase risk of infection for others in a room.


The following websites offer more information on HEPA air cleaner devices and COVID-19:

Corsi-Rosenthal DIY box filters  These Do It Yourself air filters offer a low cost option for filtering room air, but they don’t quite match the performance of a HEPA air cleaner. Materials to construct a Corsi-Rosenthal box filter include a typical 20” box fan, one or more pleated filters (preferably MERV-13 rated) to fit the box fan, and some tape to hold the filters in place.  There are different ways to construct these boxes. Here are a couple of resources:

DIY Box Filter (UC Berkeley) - link requires CalNet Authentication

How to Build A Corsi-Rosenthal Box Filter (UC Davis)