The Corsi–Rosenthal Box has been studied by engineers at UC Davis, the University of Connecticut, Portland State University, and others. The findings are consistent: this ~$40–60 DIY device delivers clean air delivery rates that rival — and often beat — commercial HEPA purifiers costing ten times more.
Key findings
Origin story
The Corsi–Rosenthal Box emerged from a practical problem: how do you improve indoor air quality at scale, affordably, using materials anyone can buy? The answer came from two engineers thinking out loud during a pandemic.
It was then refined, tested, published, and deployed by a global grassroots community — in classrooms, homes, offices, community centers, and schools — making it one of the most successful examples of open-source public health engineering in recent history.
Performance vs. cost
Clean Air Delivery Rate (CADR) measures how quickly a device can filter air in a room — higher is better. Commercial HEPA purifiers are priced with a roughly linear relationship between cost and CADR. The Corsi–Rosenthal Box breaks that relationship entirely.
At approximately $0.08 per CFM of CADR, it is 9 to 33 times more cost-efficient than comparable commercial units. For context, an EPA cost survey found commercial Energy Star purifiers range from $0.71 to $2.66 per CFM — a range entirely above what the CR Box costs.
The tradeoff is energy efficiency: the CR Box ranks lower on CADR-per-watt than some premium purifiers. For most home use this is a minor concern, but worth noting.
What it filters
MERV-13 filters are rated to capture particles down to 0.3 microns — a range that includes respiratory aerosols carrying viruses, fine particulate matter (PM2.5) from wildfire smoke, pollen, mold spores, and most bacteria.
Larger particles (10µm+) — such as dust, pet dander, and pollen — are removed at very high rates. Smaller virus-carrying aerosols (1–3µm) are removed less efficiently per pass, but the CR Box compensates with high volume: it processes far more air per hour than most single-filter purifiers.
UC Davis longitudinal testing showed the CR Box performed particularly well for particles in the 1–3µm range — the size most associated with airborne respiratory transmission.
Published research
Safety & practicalities
Beyond efficacy, researchers have studied the noise, power consumption, and fire safety of the CR Box. The results confirm it is a practical, safe device for home and school use.
The fan's power draw is essentially unchanged whether filters are attached or not — the larger filter surface area reduces resistance on the fan, offsetting any added load from the filter media itself.
Slightly quieter than a typical refrigerator. On low speed, quieter still — suitable for classrooms, offices, and bedrooms.
Comparable to the fan running alone with no filters. The increased filter surface area reduces resistance, keeping energy use low.
An EPA-funded Underwriters Laboratories study tested the design under extreme conditions and found no fire risk. Cleared for use in schools and public buildings.
Optimal placement is the center of a room, but the unit performs effectively as long as it has at least 3 feet of clearance from walls on all filter sides.
Official recognition
The research is clear. Now all you need is ~$40–60, 15 minutes, and four furnace filters.