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With the lifting of mask mandates, you may have recently seen more emphasis on proper ventilation inside businesses to help prevent the spread of the coronavirus.

However, businesses aren’t the only ones concerned about ventilation. Did you know that the average person spends 90% of their time indoors? This makes us vulnerable to indoor air contaminants – including but not limited to COVID-19.

Whether it’s protecting yourself from springtime allergies, wildfire smoke season, or illnesses like COVID, it’s good to know what to do to improve your indoor air quality. Here are some easy to follow tips.

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How can indoor air be unhealthy?

You’ve probably heard that the air outside can become polluted and unhealthy due to factors such as vehicle emissions from traffic, factory exhaust, and smoke from wildfires. However, indoor air can sometimes be even more polluted than outdoor air.

This can be due to the materials we use to build homes – such as paint, sealants, flooring, and insulation – as well as the items we keep inside, such as electronics, appliances appliances, toys, furniture, carpets and air fresheners. Indoor air can also be polluted by common indoor activities, such as smoky cooking and cleaning with chemicals. Dust is also a major contributor to poor indoor air quality. Chemicals can stick to small dust particles that we then breathe in, making them more dangerous to our health.

What happens when indoor air quality is poor?

Poor indoor air quality has both short-term and long-term consequences. In the short term, it can cause eye, nose and throat irritation, headaches, dizziness and fatigue. In the long term, it has been linked to asthma and other respiratory diseases, poorer student performance, decreased cognitive function and increased risk of chronic disease.

Who is most at risk?

The people most susceptible to poor indoor air quality are young children, pregnant women and people aged 65 and over. People with certain conditions such as respiratory disease, heart disease, kidney disease or other chronic diseases, as well as people who have or have had COVID-19, may also be more vulnerable. If you have any of these people in your household, it’s very important to see what you can do to improve the air quality for them.

The steps you can take fall into three categories:

Prevention: Prevent particles from being airborne in the first place.

Ventilation: Increase the airflow to dilute the number of harmful particles in the air.

Filtration: Filter the air to remove particles.

Prevention of poor air quality

If you are sick, congregate with visitors outdoors when possible or consider wearing a mask indoors if you must be around other people to help prevent the spread of illness. Masks can block up to 70% of droplets from the mouth and nose. The best thing you can do, however, is not to invite others into your home who are not part of your household when you are sick, and not to invite anyone who is sick or has symptoms.

Other steps you can take to avoid introducing pollutants into your home:

  • Take your shoes off inside
  • Dust and mop frequently
  • Avoid burning scented candles indoors or use candles made from 100% natural materials like beeswax.
  • Avoid using scented products like air fresheners to cover up odors
  • Avoid smoking indoors, especially around children
  • Turn on an exhaust fan or open a window when cooking

Improve ventilation

Ventilation brings in fresh air from outside to improve air circulation and dilute the number of harmful particles in your home. Opening the windows is a great idea if the weather permits. You can also place fans in a window to expel potentially contaminated air and bring in fresh air. Unfortunately, this is not a good option for communities living near major roads or industrial activities, as the air outside may already be polluted. You should also avoid opening windows during wildfire smoke events.

Examples of good and bad ventilation in the house. Image source: Source: Centers for Disease Control and Prevention (CDC)

Use whatever mechanical ventilation you have in your home: run an exhaust fan on the stove when cooking and make sure the exhaust fan is on in the bathroom when you shower. Check to see if your vent actually exhausts to the outside: unfortunately, many just vent inside, recirculating stale air back inside. If so, opening a window may help.

Indoor air filtering

Consider buying a portable air purifier with a HEPA filter, which captures and removes tiny particles from the air such as pollen, smoke, germs, mold and dust. Air purifiers vary widely in price, but some units costing around $100 can effectively clean a room.

For a more affordable DIY option, you can easily make a box fan filter at home for around $35 that can reduce certain types of air pollution by 90%. Learn more about making a DIY filter fan in this blog post or by watching the video below:

Video: Learn how to make a quick, easy and affordable box fan filter at home.

You can also build an even more efficient filter at home – known as a Corsi-Rosenthal Box – with a box fan and four 20″ by 20″ filters, as seen in the video below:

Video: Learn how to make a Corsi-Rosenthal box fan filter at home.

Use a portable air purifier or box fan filter during wildfire smoke days, when the air outside is poor, and during or after indoor activities that could impact air quality . It’s a good idea to place the filter where people spend the most time, or in places where you can’t open windows and doors or turn on an exhaust fan.

Note that portable HEPA air purifiers, box fans, and furnace filters often sell out in stores when fire season approaches, so it’s a good idea to stock up in advance.

Remember we share the air – keep it fresh and clean!

For more information visit:

  • COVID-19 Resources: Improving Indoor Air – more information and resources to share from Public Health – Seattle and King County.
  • Improving Indoor Air at Home – a webinar from Public Health – Seattle and King County with more information on improving the air quality in your home.
  • Interactive Ventilation Tool – the Centers for Disease Control and Prevention (CDC) shows you how particulate levels change when you adjust the ventilation settings in your home.
  • Certified Room Air Cleaners – an Association of Home Appliance Manufacturers website listing tested air purifiers along with the size of room they can clean and their effectiveness at removing smoke, pollen, and dust particles .
  • Certified Air Cleaners – from the California Air Resources Board, a list of units that do not produce harmful ozone.

Originally published June 3, 2022