Buzz
With parts of the Northeast shrouded in a yellow haze of wildfire smoke drifting down from Canada, many social media posts have recommended a DIY method for cleaning indoor air: a homemade purifier made from a box fan, four furnace filters, and plenty of duct tape.
Does it seem a bit rough around the edges? Yes. But is it an affordable and efficient way to clean your indoor air? Surprisingly, yes.
The invention is called the Corsi-Rosenthal Box, named after its co-creators Richard Corsi, dean of engineering at UC Davis, and Jim Rosenthal, CEO of Air Relief Technologies. The concept is straightforward: the box fan pulls air from the room through four high-efficiency MERV-13 filters, the kind used in home furnaces. The seams are sealed with duct tape, and a piece of cardboard serves as the base. The fan recirculates the air, and the filters capture dust, pollen, viruses, mold, and particles from wildfire smoke, such as acids and heavy metals.
Amanda Hu, Flickr // CC BY 2.0Corsi and Rosenthal were inspired to create an affordable air purifier during the COVID-19 pandemic in 2020. They demonstrated that the box could provide seven to eight air changes per hour in a 700-square-foot room, resulting in an 80% decrease in airborne contaminants. Filter maker 3M conducted their own tests and obtained similar findings.
In 2022, Brown University's School of Public Health conducted further research on the box's effectiveness and published their results in Environmental Science & Technology. After setting up the Corsi-Rosenthal boxes in 17 rooms, they observed a reduction of 30 to 60 percent in semi-volatile organic compounds (SVOCs). A separate study in Science of the Total Environment showed the box's performance was on par with a top-tier $549 HEPA purifier.
Why choose a DIY box instead of a commercial air purifier? The performance is comparable, but at a fraction of the cost. A box fan typically costs $20 to $25, and each 2-inch air filter runs $20 to $25, although multi-packs may offer a discount.
UC Davis provides instructions on how to build your own Corsi-Rosenthal box. While it’s relatively straightforward, ensure the filters are oriented with their arrows pointing inward to align with the airflow. The device should last several months when used for a few hours each day before the filters need replacing, though this can vary depending on air quality (you can check it using this interactive map).
The one drawback: While the boxes help cut down on air pollution, they can contribute to noise pollution. At their highest setting, box fans can increase the noise level in your room by five to ten decibels.
