Corsi-Rosenthal Box DIY Purifier: 4 Things to Know

A fan, furnace filters, and some duct tape–can air purifiers be that simple? Meet the Corsi-Rosenthal Box (CR Box) DIY air purifier. The Corsi-Rosenthal Box is a powerful, low-cost air purifier that you can put together on the cheap.

At Smart Air, we’ve been building, testing, and teaching people how to make DIY air purifiers for years. But just like the original Smart Air DIY air purifier, the Corsi-Rosenthal box has its upsides and downsides. In this article, we cover 4 things you should know about the CR box.

1. The Corsi-Rosenthal Box is a powerful air purifier, with low upfront costs

Tests show a Corsi-Rosenthal box can achieve a clean air delivery rate (CADR) of 165-239 cubic meters per hour at a cost of around $75. That makes the CR box air purifier one of the best bargains on the market. 

2. Less effective at removing virus droplets from the air

One downside is that CR boxes use MERV 13 filters, which capture a lower percentage of virus-sized particles on a single pass than HEPA filters. MERV 13 filters capture around 85% of COVID-19 droplets, while HEPA filters often capture over 99.95%. However, the CR box moves so much air that it will capture many of those particles on the second pass and the third pass. That explains how it outperformed the IQAir with much higher-rated filters in a head-to-head test.

3. In the long run, the Corsi-Rosenthal Box fan may cost more

One of the primary reasons people turn to the Corsi-Rosenthal Box is the low up-front cost. In almost all cases, they are cheaper than buying an off-the-shelf any air purifier that is equally strong. In fact, Smart Air designed its own DIY air purifiers back in 2013 for the exact same reason.

However, if we consider long term usage and costs over time, although other air purifiers may cost more upfront they can actually work out cheaper than the CR box in the long run. Why? The CR Box uses more energy and costs more to replace filters.

Open Data: We have made the long-term cost analysis data for the Corsi-Rosenthal Box openly available.

4. The Corsi-Rosenthal Box may be too noisy for many environments

Tests showed the Corsi-Rosenthal Box can be noisy–with some models reaching 67 decibels on the high setting. Any level of noise over 60 decibels is likely too noisy for most settings, such as schools and offices. Classrooms tend to be around 45-50 decibels, so 60 decibels would overpower a class. Running the CR Box at lower speeds will lower noise but also reduce the amount of air it cleans. Bit fans and large HEPA filters are what can keep purifier noise down, like those in the Blast air purifiers Smart Air has designed.

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