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Clean Air 

Clean the air we share indoors!

The viruses that cause COVID-19 and the flu spread much easier indoors. Ventilation and filtration help by removing allergens, asthma triggers, and dust from the air. To reduce spread of viruses, combine use of these filters with other protections like masks, distancing and vaccination. Safer indoor air has many health benefits, including reducing the risk of getting sick with COVID-19.


Make indoor air safer by combining these ventilation and filtration best practices:

  • Open windows and doors (when possible) to let in fresh air.
  • Turn on fans to circulate the air inside your space.
  • If the space has an HVAC system, switch your blower to “ON” vs “AUTO” to allow air to blow continuously.
  • Use a Portable Air Cleaner (HEPA or CR Box) to filter the air in your space.
    • Buy HEPA filter at a store or online. Choose a filter that is the right size for your space. You can refer to the EPA's Air Cleaner Guide for more information.
    • Build a Corsi-Rosenthal Box (CR Box), a DIY air filter that provides clean air to your space at an affordable cost.
      • A CR Box uses everyday items found in hardware stores, is easy to make, affordable, and helps your space have safer indoor air. Experts on indoor air quality invented this box so many people could have access to clean air in the rooms they use daily.This box can have an immediate impact on your health, and, because it is a fraction of the cost of commercial HEPA filters, units can be installed and clean the air for more people.
  • Take other recommended public health actions, such as staying home when you are sick, wearing high-quality masks, and staying up-to-date on vaccinations.


For more information on how to build a box yourself, check out this guide from UC Davis or check out these resources from the Clean Air Crew


CR Box Build Instructions Clean Air Informational Flyer


Filters must be replaced every 6 to 9 months

  • The fan can be used to create a new CR Box, but the filters need to be replaced every 6 to 9 months or when obviously dirty.
  • When it's time to replace the filter...
    • Be sure not to release any dust.
    • Let them sit with the fan off for 2 days.
    • Carefully cut the duct tape and place the filters in a large trash bag without crushing or bending the filters.
    • Seal the trash bag. Wipe down the fan with a wet paper towel or baby wipe before reusing.

Clean Air Resources

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