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Expecting Guests? How to Make Your Own COVID-Fighting Air Purifier

November 30, 2020

With small-house gatherings now the greatest source of COVID-19 spread as America moves indoors, according to the Centers for Disease Control and Prevention, it’s time to start thinking about your home’s air exchange rate and how you can minimize your guests’ exposure to airborne viral particles.

Don’t put away that summer box fan yet if you’ve decided not to follow the CDC’s recommendation that the safest gathering is either virtual or restricted to immediate household members.

Let’s leave the specifics of air exchange rate to your local HVAC professional, but the average home replaces two-thirds of indoor air every two hours or so. It takes about six hours to replace all air in the home. Many homes use a furnace filter to circulate air while removing dust and other small particles from their forced-air heating and cooling system. Most systems are installed with a basic MERV-8 filter, which removes only larger particles. The Environmental Protection Agency recommends a filter with a Minimum Efficiency Reporting Value of 13, or MERV-13, to improve a furnace’s capacity to remove viruses from circulated air.

If you have such a system, install a MERV-13 filter and run the fan continuously when you have guests. If you don’t have a forced-air system, improvise. Air purifiers work (click here for information on why you should be using a HEPA air purifier and humidifier this winter), but they can be expensive. For a simple, do-it-yourself alternative, strap a MERV-13 to the intake side of a box fan. You’ll get even better performance with a filter on both sides of the fan, though a single filter should work.

But you’ll need more than an air purifier to protect your guests.

“Increasing evidence shows there is increased transmission of the virus in crowded (close proximity), enclosed and poorly ventilated spaces for prolonged durations,” says Dr. Faiqa Cheema, a Hartford HealthCare infectious disease specialist.

The World Health Organization recommends six air exchanges per hour with up to four people in a 10-by-10-foot room. You’ll need some simple ventilation  — open at least one window in the room. Use a window fan to remove air from the room, too. If you have a bathroom fan, make sure your guests use it.

Comfort is the other part of the equation. With windows open, you might need to crank up the heat. But leave the windows open for at least an hour after your guests leave to ensure a safe air exchange that removes any lingering viral particles.

The rest is up to you: Wearing a mask, maintaining safe distancing and frequent hand sanitization will make your gathering even safer.