Removing infectious aerosols and wildfire smoke particles from indoor air has been a DIY, community-led project since August 2020, when Dr. Richard Corsi and Jim Rosenthal designed the Corsi-Rosenthal Cube. Now colloquially known as a Corsi box, these DIY air purifiers have been adapted by indoor air quality (IAQ) experts and validated as an effective air cleaning method by several peer-reviewed studies. They’re easy to make and they work better than some commercial units!

The robust performance of Corsi boxes is largely due to the electrostatic charge (which attracts particles) and large surface area (pleated/accordioned into a compact size) of ordinary MERV-13 filters you can buy at any hardware store.

Over the past three years, Corsi boxes have enjoyed major community uptake and an open source design evolution largely documented on Twitter (now X). These DIY designs have been accompanied by community CO2 measurement education (see Make:’s “Plan CO2” series) and new open source databases about IAQ in public spaces.

Our organization, Open Source Medical Supplies (, has been diligently curating the Corsi box research and design ecosystem into our project library. Here is a simple breakdown of current Corsi box designs, their build cost, and user tools to evaluate the best project for your indoor setting.

Why Do I Need a Corsi Box?

Clean air delivery rate (CADR) of various DIY air cleaner designs, measured by researchers at U.S. Environmental Protection Agency.

Clean indoor air is an important element of public health. Exposure to airborne pathogens and particles such as dust, smoke, mold, and pollen can negatively impact heart, lung, and brain function, and spread infectious disease. In rooms with poor ventilation, harmful particles can linger for hours or even days without an effective air purifier. The large cleaning surface area of MERV-13 filters makes Corsi boxes a more thorough and rapid purifying solution when compared to some commercial units.

How Does It Work?

Basic Corsi-Rosenthal cube design: Dirty air is drawn through four filters around the sides, clean air exits the top. Illustration by Amanda Hu, CC BY-SA 4.0

A Corsi box draws in contaminated air through the filter sides, and emits clean air through the top (above). This clean air then circulates through the room while the purifier continually cleans more air. An alternate design emits clean air through one side (below).

Alternate Corsi-Rosenthal cube design: Dirty air is drawn through four filters, clean air exits one side. Illustration by Amanda Hu, CC BY-SA 4.0

How Do I Measure the Effectiveness of a DIY Purifier?

Proposed Non-infectious Air Delivery Rates (NADR) for Reducing Exposure to Airborne Respiratory Diseases; The Lancet Covid-19 Commission Task Force on Safe School, Safe Work, and Safe Travel

Clean air delivery rate (CADR) describes how much clean air the purifier is emitting. This measurement, combined with a given room size, determines air changes per hour (ACH), which defines how many times per hour the volume of air in a given space is replaced with recirculated air. The Lancet Covid-19 Commission recommends a minimum of 4 to greater than 6 ACH to reduce exposure to airborne respiratory diseases. 

Why Can’t I Just Use a Commercial Air Cleaner?

You can. Clean Air Stars’ open source calculator at can help you pick an adequate commercial air purifier. DIY air purifiers are sometimes more affordable, more portable, and have a greater cleaning filter surface area when compared to some commercial units, especially during wildfire smoke events. They also make great STEM classroom projects!

Project Steps

Box Fan Corsi Boxes

Original Corsi-Rosenthal Cube

  • Time Required: 30–60 Minutes
  • Difficulty: Easy
  • Cost: Under $100

The “OG” Corsi-Rosenthal Cube is built with a 20″ box fan, duct tape, and four 20″ MERV-13 filters.

Shiven Taneja has provided excellent build guides in English, French, German, and Spanish, including a mini-Corsi box and UK-specific instructions. These include a cardboard shroud that narrows the fan flow slightly to reduce backflow; you can make it for free, from the box the fan came in.

Pros & Cons: Box fan Corsi models are the cheapest and easiest-to-build DIY air purifiers, with an easily sourced BOM and short build time. They are the quickest to deploy in an airborne contaminant emergency, such as wildfire smoke. However, when operated on the highest setting the box fan Corsi can be loud, causing it to be turned off in high-risk indoor areas. The louder the fan, the more likely it is to be turned off. The most effective cleaner is the one that’s actually running.

PC Fan Corsi Boxes

As Corsi boxes became more common, researchers identified a demand for quieter models with a lower decibel (dB) rating to encourage people to keep the purifier running in settings where transmission risk is highest, like indoor rooms with multiple people, including classrooms. This need, along with the preference for a more compact design, catalyzed the development of versions using PC fans.

Wissman Corsi Cube

  • Time Required: 2–3 Hours
  • Difficulty: Moderate
  • Cost: $140–$150

One of the earliest and most popular PC fan Corsi boxes was created by Rob Wissman using five PC fans and four Ikea Starkvind filters, and shared on GitHub.

Wissman’s cube-shaped build inspired the most popular current models — the compact, portable, two-filter rectangular PC fan air cleaners. Due to their small floor footprint and almost-inaudible fan noise, PC fan designs continually clean the air without creating auditory disruptions. Joey Fox, IAQ Advisory Chair for the Ontario Society of Professional Engineers (OSPE), has curated several of these designs, all featuring detailed build instructions with diverse frame materials.

Azevedo Corsi Box

  • Time Required: 2–3 Hours
  • Difficulty: Moderate
  • Cost: $150–$220

Check out this slim two-filter Corsi box built by Matthew Azevedo, who has shared complete build instructions at It’s Airborne. A remix of the Wissman build, it features six P14 fans and two Ikea Starkvind filters for quiet operation and sleek design. To save money, you can use five fans and downgrade them to the quieter P12 type.

Corsi Kits

Clean Air Kits STEM Panel Kit

  • Time Required: 30 Minutes
  • Difficulty: Easy
  • Cost: $174–$309

Clean Air Kits offers DIY STEM kits for home or classrooms, including PC fans and all necessary components except for the filters, which the purchaser must source. A filter selection guide is provided on their site at


Breathe Free!

With your DIY Corsi box air filter you’re ready for the next wildfire or Covid outbreak. Or if you wish, you can run it all the time to upgrade IAQ in your home or workplace.

Filters and Wildfire

Indoor air filters typically last months, but the EPA recommends more frequent filter changes for air purifiers exposed to wildfire smoke. The filters should be replaced when they are dark-colored or smell like smoke.

Helpful Links