The Corsi-Rosenthal Box is a build-it-yourself air purifier. The original design was drafted by engineers Richard Corsi and Jim Rosenthal during the COVID-19 pandemic and is pretty basic, consisting only of four furnace filters duct-taped together and supporting a large box fan. Overall performance and feature sets can vary depending on what components you use. However, as long as you stick to using high-quality filters and a relatively potent box fan, your own build will return broadly similar results. We built our own Corsi-Rosenthal box using this guide.
Our Verdict
Our Corsi-Rosenthal Box is a good fit for pet owners. While it's exceedingly noisy and will likely be a source of anxiety for animals that are particularly sensitive to loud noises, it also does a fantastic job of trapping a variety of particle sizes, including pet dander.
- Superb overall particle filtration performance.
- Very high clean air delivery rate.
- Very noisy.
A Corsi-Rosenthal Box might not be the best choice for use in bedrooms. Depending on your filters and fan, these can be large, ugly, and very noisy machines. They do a fantastic job of trapping most airborne particles and are highly effective in larger spaces.
- Superb overall particle filtration performance.
- Very high clean air delivery rate.
- Very noisy.
- No smart functionality or sleep mode.
A Corsi-Rosenthal Box with this design has a remarkably high particle filtration rate. An appropriately sized box fan generates sufficient airflow to quickly clear the air of particulate matter even within very large open concept living spaces, to the point of it being overkill for most households. Combined with its bulky footprint and high operating noise, it's mainly a good fit for really big areas where aesthetics aren't a big concern, like workshops or garages.
- Very high clean air delivery rate.
- Very noisy.
Changelog
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Updated Feb 11, 2026:
We've updated the text in this review to reflect new tests added with version 1.1 of our test bench.
- Updated Feb 11, 2026: Version 1.1 of our air purifier testing methodology provides a more representative summary of unit performance, with a revised Particle Filtration Rate test conducted in a better-sealed environment and a more reliable means of generating consistently sized particulate matter. We've also included a parameter for the machine's maximum recommended room size. For a more detailed breakdown of the changes made, see our full changelog.
- Updated Nov 04, 2025: Version 1.0.2 of our Air Purifier Test Bench rectifies calculation errors in our existing Particle Filtration Rate test to provide more representative results of some units. For a more detailed breakdown of the changes made, see our full changelog.
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Updated Aug 28, 2025:
We've updated the link to the how-to guide for this air purifier.
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Differences Between Sizes And Variants
Since this is a build-it-yourself device, overall performance can differ depending on component choice. It's worth noting that we tested a single-filter variation of the Corsi-Rosenthal Box, and it returned a drastically different overall performance.
Popular Air Purifier Comparisons
It can be difficult to compare a Corsi-Rosenthal Box to most commercially available alternatives out there; as we determined in our research and development process, this homemade solution is very effective when it comes to particle filtration specifically because it doesn't have to follow the trends that dictate normal air purifier design, like size, noise, and even aesthetics. If you plan on using a Corsi-Rosenthal Box in an area where none of those things are a significant factor, it's certainly worth building your own.
Test Results
The Lasko 20-inch box fan in our Corsi-Rosenthal box has a three-level fan speed adjustment dial.
Our Corsi-Rosenthal Box's filter system consists of four 3M Filtrete 20x25x1 MPR 1900 Premium Allergen, Bacteria & Virus Smart Air Filters. These filters have an estimated lifespan of three months when used in a home furnace, air conditioning, or HVAC system; their lifespan in an air purifier will fall within a similar ballpark, depending on how often you run it. You can get a pack of four here.
This iteration of a Corsi-Rosenthal Box has a remarkably high particle filtration rate. Its CADR is sufficient for it to be an effective, efficient option even within large, open concept spaces.
This is a very loud air purifier. Even at its lowest setting, a 20-inch box fan produces a noticeable hum that can be distracting if you're having a conversation nearby. At its highest fan speed, it'll make it almost impossible to hold a conversation without drastically raising your voice.