Help reduce the spread of COVID-19 by improving indoor air this fall and winter

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By now you may have heard that we’re experiencing high cases of flu and RSV (a respiratory disease) (in-language resources available) this fall, with young children being hospitalized.  With cold weather, we spend more time inside. This increases the potential for another surge of COVID-19 cases and hospitalizations in the coming months.

Diseases like RSV, the flu, and COVID-19 are airborne and spread easily indoors. With that in mind, it’s important to pay attention to indoor air quality.

Over the fall, Public Health recommended shutting windows to keep wildfire smoke outside. To reduce the germs that cause respiratory illnesses, you want to do the opposite. Bring in as much fresh outdoor air as you can. Below are some strategies for how to do just that!

It’s important to remember that indoor air quality is just one of the many prevention strategies to prevent COVID-19. Other strategies to protect you, your loved ones, and your community include:

Strategies for improving indoor air

Two key strategies for healthy indoor air are ventilation and filtration. Ventilation pulls fresh outside air into indoor spaces to reduce the amount of airborne pollutants, such as viruses. Filtration removes viruses and pollutants from the air by trapping them in a filter.

The actions listed below will help you improve both ventilation and filtration in your home, business, workspace, school, community space, or any other place you may gather indoors with others.

Four key actions for improving indoor air

  • Open a window or door (if the weather allows and if it is safe) – even just a few inches can improve your indoor air! Place a portable fan by the opening, facing out, to blow potentially contaminated air out. Unfortunately, this may not be a good option for some communities. For communities living next to major roads or industrial activities, outside air may be more polluted.
Image of a room with particles in the air. The windows are open to bring fresh air in and a window fan is blowing the particles from inside the room out through the window.
Opening windows can help improve your indoor air quality. A window fan can help push bad air out and draw in fresh air. Image credit: What Else Design
  • Run exhaust fans like bathroom fans or kitchen hoods. These fans can help remove stale air and pull in fresh outdoor air.
  • Consider buying one or more portable air cleaner(s) with HEPA filters. HEPA filters capture and remove tiny particles from air such as germs, pollen, smoke, mold and dust. Air cleaners vary in price, but some units costing around $100 can effectively clean a room. Read our HEPA cleaner guidance (this webpage is in English only) for more information on how many to use depending on the size of your space and what certifications to look for. (Worried about energy use? HEPA air cleaners on their highest setting use about as much energy as one light bulb!)

    For a more affordable DIY option, you can easily make a box fan filter at home! This option costs as little as $35 and can reduce certain types of air pollution by 90%. We have a quick video you can watch (this webpage is in English only) to learn how to make a box fan filter. Use a thicker, 2” or 4” filter for better protection. The best option for filtering COVID-19 is to make a cube using multiple filters and a box fan.

    For both HEPA cleaners and box fan filters, maintenance is critical to ensure they’re running properly. Be sure to replace filters regularly according to your unit’s maintenance schedule. Replace filters used with box fans every three months or when they look dirty. Note: Using a filter or air cleaner doesn’t replace other ways of improving ventilation, like opening windows or running fans. Filtration and ventilation actions work together to reduce exposure to airborne diseases.
Image of a room with a few particles in the air and a HEPA air cleaner removing particles from the air. The windows are closed.
Using mechanical filtration such as a HEPA filtration unit can reduce up to 99% of the particles in the air. Image credit: What Else Design
  • Do you have a Heating, Ventilation, and Cooling (HVAC) system? If so, there are a few key actions to take:
    • Upgrade the filter in your system to MERV 13, or the highest rating your system allows.
    • Open the dampers (moveable vents) to let in more outside air. Try to increase the amount of outdoor air it pulls in to 100%.
    • Create a schedule for regular HVAC inspections, cleaning, and maintenance. Include filter replacements and system upgrades or improvements in the schedule.
    • Not sure if you have an HVAC system? Ask your facilities or building manager for more information. When you do, you can ask about the strategies listed above.

What should I look for?

If you’re visiting public spaces, there’s a few things you can look for to tell you about the quality of indoor air.

  • Is the air still? If so, that’s a likely sign there’s not good air flow.
  • Look to see if there are open windows or doors that allow air to move in and out of the space.
  • Are there HEPA air cleaners or box fans with filters attached – and are the devices turned on?
  • Can you see signs of an HVAC system, such as vents or ducts?

What is Public Health doing?

Are you a business or organization that is open to the public? Public Health offers free technical assistance to help you improve your ventilation and indoor air quality. To request assistance, please complete this form (in-language resources available) to the best of your ability. Our staff will respond as soon as possible. If you need help with the form or an interpreter, please email or call 206-477-5166. Interpretation available by stating your language in English. Then, please hold while you’re connected to an interpreter.

Additionally, we offer more resources on our Indoor Air Quality webpage (in-language resources available). This page contains:

  • more strategies to improve indoor air quality.
  • reference documents available in multiple languages.
  • specific guidance for different settings: shared or congregate housing, schools and child care facilities, and restaurants.

Originally posted on 12/13/22