Tools to build a Corsi-Rosenthal filter

The Corsi-Rosenthal box is a do-it-yourself method of building an air purifier. The few tools needed are filters, a box fan, scissors, duct tape, and cardboard.

Does exposure to certain irritants trigger your lingering cough or cause breathlessness? Lungs still recovering from COVID-19 may be affected more during wildfire season, according to Laren Tan, MD, a pulmonologist and chair of the Department of Medicine at Loma Linda University. He says home air purifiers are a great resource to limit exposure to debris and air contaminants, but this precautionary measure can cost a pretty penny. Luckily, a simple at-home project, supported by experts, can be just as effective.

According to the CDC, exposure to air pollutants in wildfire smoke can irritate the lungs, cause inflammation, alter immune function, and increase susceptibility to respiratory infections, including COVID-19.

In conjunction with proper home cleaning techniques, research shows that air filters can help to remove particles that irritate the lungs from indoor spaces. Harmful particles removed with proper filtration include allergens, smoke, and mold. The study states that the attributes of an air filter are:

  • Airflow to assure adequate ventilation
  • Efficiency to filter out a range of small particle sizes, and
  • The capacity allows for reasonably cost-effective maintenance schedules without adversely affecting airflow and efficiency.

The Corsi-Rosenthal box is a do-it-yourself method of building an air purifier that follows the above three attributes. Supplies needed include four MERV 13 filters, one box fan, scissors, cardboard, and duct tape to seal the assembly.

  1. Build the shell by connecting all four filters together with duct tape and have all arrows pointing in with vertical pleats on the filter. To ensure all air goes through the filter, seal all edges with duct tape. Step 1
  2. To create the “floor” of the Corsi-Rosenthal box, tape cardboard on one end of the cube, leaving one end open. If using a new box fan, keep the cardboard box it came in for this step.Step 2
  3. To further improve the efficiency, create a fan shroud by covering the corners. See Jim Rosenthal’s article about the optional step here.Step 3
  4. For the final side, place the box fan on top of the structure and seal all openings with duct tape.Step 4

“People in the inland region are especially exposed to air pollutants due to the prevalence of wildfires in the area,” Tan says. “It’s essential to do what you can to protect your lungs when recovering from COVID-19 infection.”

Loma Linda University Health continues to follow strict COVID-19 safety measures in our hospitals and clinics, so you can feel confident when you need care. For information and updates on coronavirus, click here.