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Wildfire, fire management and air quality news for western Montana and the Northern Rockies.

DIY home air filters can be effective and safe, researcher says

Tom Javins holds a HEPA filter used in a DIY home air filter. Javins says his tests show the DIY filters can be safe and effective.
Courtesy Amy Cilimburg
Climate Smart Missoula
Tom Javins holds a HEPA filter used in a DIY home air filter. Javins says his tests show the DIY filters can be safe and effective.

Researchers are increasingly concerned about the public health impacts of wildfire smoke.

A Montana engineer researched the efficacy and safety of an inexpensive and increasingly popular "do-it-yourself" home air-filtration system.

[This story was originally published in August of 2020]

Montana lucked out this summer. Despite persistent early-season warnings of an above-average fire potential, June, July and most of August brought us low fire activity and clear air. But luck ran out last week after California’s wildfire smoke started drifting into Montana’s airshed.

"What has kept a lot of us up at night this year has been that potential at the intersection of COVID and wildfire smoke," says Amy Cilimburg, executive director of the Missoula-based Climate Smart Missoula.

According to the federal Centers for Disease Control and Prevention, wildfire smoke can irritate your lungs, cause inflammation, affect your immune system, and make you more prone to lung infections, including the virus that causes COVID-19.

Since the catastrophic wildfires of 2017, Climate Smart Missoula has teamed up with the local health departments to loan or donate hundreds of portable High Efficiency Particulate Air (HEPA) air purifiers to schools, daycares and vulnerable residents who otherwise can’t afford them. The machines improve indoor air quality and are especially appreciated when the wildfire smoke intensifies. They can set you back anywhere from $100 to $1,000, but there is a cheaper alternative.

"You can get an effective room air cleaner that you can make yourself for between $35 and $45," says Mechanical Engineer Tom Javins.

Javins didn’t come up with the concept of using a bungee cord or duct tape to attach a high-quality air filter to a box fan to create an effective, budget friendly air purifier.

"But no one had looked at how effective they were for filtering or how safe they were, so that’s what I was interested in doing."

Fireline probes the causes and consequences of the increasingly devastating wildfires burning in the U.S. It taps into the experience of firefighters, tribal land managers, climate scientists and more to understand how we got here and where we're going.

Javins is the former Associate Director for Engineering and Utilities at the University of Montana and has over 30 years of heating, ventilation and air conditioning experience.

He volunteered to test these devices, and he says the results were encouraging.

"These can be equivalent to a small- to medium-room air purifier with a HEPA filter in them; reasonably effective for a much lower cost," he says.

He convinced other experts to run their own tests.

"I actually had 3M Products group test a box fan filter in their chamber that they test room air purifiers. They verified the data I was seeing, so I felt pretty good about the effectiveness of the filter."

But almost three years ago when acrid wildfire smoke settled in like fog over western Montana’s valleys, Javins say Missoula health officials were reluctant to endorse use of these homebrew air purifiers. He says they worried box fans with filters would reduce airflow to the point where they could potentially overheat and catch fire. Almost 5 million box fans were recalled in 2011 due to an electrical failure in the fans’ motors. Those problems were fixed in fans sold after 2012.

This winter, Javins ran a battery of controlled torture tests on newer-model box fans to determine just how safe they are. He concluded the risk is miniscule.

"I ran those for two weeks with the air flow blocked off on one side — basically a filter totally plugged — and the temperatures did not exceed the manufacturer's limits for the motor. They were well under that."

Anyone interested in building their own air purifier is advised to use a new fan, keep it away from curtains and loose clothing and keep the fan and its motor clean. These steps reduce fire risk.

Climate Smart Missoula’s Amy Cilimburg says Javins’ research is deeply appreciated. Cilimburg feels comfortable recommending these do-it-yourself fan filters. Even if Montana’s air is starting to clear, she says it’s never too late to prepare for future smoke events.

"It’s going to take years for us to think about how we have healthier homes, how we help folks that are most vulnerable, how do we help improve homes that may need to be weatherized and may need energy efficiency upgrades so that they’re not so leaky. There’s opportunities for us to grow and build these efforts over the years."

Specific instructions and necessary materials to build do-it-yourself box fan/filter room air cleaners, plus a ton of other tips to help create cleaner indoor air can be found at

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Edward O’Brien first landed at Montana Public Radio three decades ago as a news intern while attending the UM School of Journalism. He covers a wide range of stories from around the state.  
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