How To Check If You're Ventilating Indoor Spaces Properly

How To Build Your Own Air Filter At Home
Photo credit ByoungJoo/Getty Images
By KCBS All News 106.9FM and 740AM

There has been much discussion about how to properly ventilate and dilute air in indoor spaces in order to reduce transmission of the novel coronavirus through aerosols.

But how do you check if your set-up is actually working?

"A simple way we’ve been sharing with the public is to buy a carbon dioxide detector," said Dr. Shelly Miller, professor in the College of Engineering and Applied Science at the University of Colorado in Boulder on KCBS Radio's "Ask An Expert" segment Thursday.

Dr. Miller said carbon dioxide detectors are readily available online and cost about $100 each.

While some people may be concerned if they see condensation building up on windows, for example on public transit or in a shared car, Dr. Miller explained moisture operates somewhat differently and is not necessarily a good indicator of aerosol flow.

A carbon dioxide detector, on the other hand, can give people a good idea of whether or not exhalation is building up in a shared indoor space.

"If you monitor the carbon dioxide in a space and you keep it below - I’m saying 600, 800 parts per million, outside is 400 - if you keep it below that, you can use it as a proxy for how much exhaled CO2 is being released into your classroom by the people who are in the room," Dr. Miller explained. "And if that is building up, that means you’re not getting enough outside air to dilute that carbon dioxide."

Carbon dioxide levels should indicate whether or not air is being properly diluted, whether through filtration or ventilation. They do not, of course, detect for the presence of the virus itself.

In normal situations, 1,000 ppm is a recommended level for carbon dioxide, "but I’m being cautious and saying let’s aim for 600-800 if we could," she said.

Most spaces are generally well mixed so readings should be fairly consistent throughout a space, unless you are close to a concentration of people or breathing on the detector.