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.

Corsi-Rosenthal Box: Four Things to Know

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

Tests show a $75 Corsi-Rosenthal box can achieve a clean air delivery rate (CADR) of around 165-239 CFM. Other tests even show a DIY CR box reaching a CADR of 850 CFM. That makes the CR box air purifier one of the best bargains on the market. 

2. Less efficient 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.

Corsi-Rosenthal Box Merv 13 Filters

3. Possible higher running costs

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 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, the UC Davis estimate of the CR Box energy efficiency of 2.17-2.19 CADR/watt ranks last compared to 23 popular air purifiers. Results vary significantly between studies though, with one study showing significantly better efficiency. Using a more efficient box fan may help lower energy costs. Energy usage of an air purifier is an important factor that should be considered when calculating the cost of operating an air purifier.

Read More: The Hidden Cost of Air Purifiers

Open Data: Long-term cost analysis data for the Corsi-Rosenthal Box 

Corsi-Rosenthal Box: Cost Analysis

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. Big fans and large HEPA filters are what can keep purifier noise down, like those in the Blast air purifiers Smart Air has designed.

Corsi-Rosenthal Box: Noise Levels

Bottom Line: Pros and Cons of the Corsi-Rosenthal Box DIY Air Purifier


* Lower upfront costs
* High cost-effectiveness ratio
* Fun, science-backed DIY project for school kids


* Can be noisy on high
* Low small-particle filtration efficiency rates (when using MERV)
* Energy costs may be higher compared to some air purifiers on market

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