DIY Clean Air: Building a Corsi-Rosenthal Box for Emergency Preparedness

Click to share this on facebook.Click to tweet this blog post.
Woman with her chin angled upward up with her eyes closed. The Where It's AT Ability Tools Blog logo with text underneath that reads "DIY Clean Air: Building a Corsi-Rosenthal Box for Emergency Preparedness, AbilityTools.org"

When wildfires or other air quality emergencies strike, having access to clean air is essential for your health and well-being. (Be sure to check out your area’s Air Quality Index). The Corsi-Rosenthal box is a simple, low-cost DIY air purifier that can help improve indoor air quality using everyday materials. The box was invented by Richard Corsi, the dean of engineering at the University of California, Davis, and Jim Rosenthal, the CEO of filter manufacturer Tex-Air Filters. Following the guide, “Science in Action: How to Build a Corsi-Rosenthal Box” published by UC Davis Engineering, we will help walk you through the building process step-by-step to help you stay prepared and breathe more easily during emergencies.

Four white square air filters formed into a cube shape. A box fan on the top part, a cardboard sheet cut out with a circle above the fan. A cardboard sheet in a square is on the base of the cube. Text underneath reads "Illustration by Amanda Hu"
A cube with a box fan on the top. Red tape is shown on the corners of the cube and on the top of the box fan. Blue lines shoot out of the top of the fan. Black arrows are pointing toward the sides of the cube inward.

This box is made with simple materials found in your local hardware store. The box fan pulls air through the filters on the sides and blows out clean air. This has been proven effective in reducing exposure to airborne particles, including virus-containing particles like COVID-19 and harmful wildfire smoke.

Section #1: Gather Materials

Materials List:

Square with four white borders  and a grate in the middle.
Square fan with blades in the middle and a grate over the blades. There is a handle and button on the top of the fan.
Brown cardboard box with a black outline
  • Box Fan’s Cardboard Box or Any Available Cardboard
A pair of scissors with blue handles
A yellow and grey utility knife

Utility Knife

A red tape roll with a white circle in the middle
A black tape measure with blue buttons and text that reads "ProTape 16', Talking Tape Measure" Yellow tape measure pulled out to 2 inches in length.

Section #2: Form the Cube

Hands hold a rectangular air filter with vertical stripes down the middle of the grate.

1. Identify the Filters: Locate the four rectangular air filters, each with a long and short side.

  • Understand Orientation of the Filters:
    • Hold one filter so that its long side is vertical (standing upright) and its short side is horizontal (facing outward). This is the position for all filters in the box-like structure.
Four square air filters with white borders and grates in the iddle are shown in a cube-like structure.
  • Remember: There will be arrows on the filter. Feel for raised or textured markings where the arrow is printed. Ensure that they are facing inward when forming your box shape.
A blue and white arrow on a white border with vertical stripes in the middle of the border.

2. Start Forming the Box Shape:

  • Position the Filters:
    • Place the first filter flat on the surface in front of you with the long side facing upward and away from you.
    • Position the second filter vertically on the left edge of the first, so it forms a right-angle corner to the left. The two filters should meet along their long sides.
    • Place the third filter vertically on the right edge of the first filter, and mirror the position of the second filter on the left.
    • Place the fourth filter across the top, connecting the tops of the second and third filters.
A white square with off-white borders. Each border has an arrow pointing inward. A blue circle zooms in on one arrow showing it pointing inward.

3. Continue Building the Cube:

  • Gently trace along the edges of the filters to ensure they meet at right angles and form a symmetrical, box-like shape.
  • Secure the Structure:
    • Use duct tape to firmly wrap around and seal each of the four connecting edges on the outside to hold the cube-like shape in place.
Two white square air filters with grate inside and white border placed perpendicular to each other. A pair of hands uses a red duct tape roll on the intersection of the air filters
A white cube made of rectangular air filters with red tape on the outer corner intersections of each filter.

Section #3: The Base

A white cube made of rectangular air filters with red tape on the outer corner intersections of each filter.  A brown square is place atop the cube and black arrows point down towards the brown square.
  • Prepare the Base:
    • Use one side of a sturdy cardboard box placed under the cube’s base.
    • Cut the cardboard along the outer edges of the cube to fit snugly at the base of the cube structure.
A white cube made of rectangular air filters with red tape on the outer corner intersections of each filter.  A brown square is place atop the cube. A pair of hands hold red tape  at the intersection of the brown square and cube.
  • Attach the Base:
    • Place the cardboard piece under the cube.
    • Duct tape the cardboard on the outer corners to all four sides of the cube to secure it firmly.
A white cube made of rectangular air filters with red tape on the outer corner intersections of each filter and a brown square atop the cube.

Section #4: The Fan

  • Position the Fan:
    • Place the fan on top of the cube with the airflow direction facing upward, so air blows out of the top.
A cube made of air filters with red tape on the intersection of each filter. A white box fan is placed atop the structure facing up.
  • Seal the Fan:
    • Use duct tape to seal all edges where the fan meets the cube to prevent air leakage.
    • Ensure the corners are securely sealed.
A white cube with red tape on the outer corners and box fan placed facing up atop the cube. a pair of hands hold a red roll of duct tape at the intersection of the fan and cube.
  • Seal Additional Openings:
    • Check for any holes or gaps on the sides of the fan housing.
    • Seal these off with duct tape to maintain optimal airflow efficiency.
A white cube with red tape on the outer corners and box fan placed facing up atop the cube.  a blue circle is zoomed in on a corner showing the cube and fan covered by the same piece of red tape

Section #5: The Shroud

  • Cut the Shroud:
    • Use a sturdy sheet of cardboard and a utility knife.
    • Cut around the outside border of the fan to fit snugly over the top of the fan.
  • Measure and cut a circular hole in the center of the cardboard (approximately 15 inches in diameter for a Lasko Box Fan).
  • Tip to Measure a Circle:
A brown square with rounded corners and a white circle in the middle
  • Attach the Shroud:
    • Place the shroud over the top of the fan.
    • Secure it by taping all four sides horizontally to the fan edges with duct tape.
A brown square with rounded corners and a circle with fan blades and grate in the middle.
A white cube with red tape on the corners with a fan placed facing up atop the cube. a brown square with rounded corners  with a hole  in the middle is atop the fan. A pair of hands hold red duct tape at the intersection of the brown square and top of fan.
  • Plug in the device and place in the middle of a room:
    • You should place a Corsi-Rosenthal box in the middle of a room on a table or cabinet to allow for efficient airflow.
    • Avoid placing it on the ground, in corners, or against walls.

In times of poor air quality, a Corsi-Rosenthal Box can be a simple and effective tool to help protect your indoor environment. By following these steps, you can build a cost-effective air purifier to improve air quality and support healthier breathing during emergencies. Stay prepared, stay safe, and breathe easier knowing you have a reliable solution at hand. For more resources check out CFILC’s Disability Disaster Access & Resources Program which assists individuals with disabilities and older adults in disaster readiness and recovery.