Corsi-Rosenthal box
Reddit take
AI summary of the Reddit excerpts below — not a quote
The Corsi-Rosenthal box is a highly effective, DIY air purifier made from a box fan and MERV 13 or 14 furnace filters. It is widely praised on Reddit for providing a Clean Air Delivery Rate (CADR) that rivals or exceeds expensive commercial units at a fraction of the cost. While it is a favorite for budget-conscious users and those dealing with smoke or heavy dust, it is frequently criticized for its industrial appearance and high noise levels when using standard box fans.
Pros
- High Clean Air Delivery Rate (CADR) for large particulates and smoke
- Significantly more affordable than high-end commercial HEPA purifiers
- Highly effective for visible dust capture
- Customizable designs, including quieter versions using PC fans
Cons
- Large, bulky footprint that takes up significant floor space
- Standard box fan versions are often too loud for quiet environments
- Homemade aesthetic may not suit living areas or shared spaces
Caveats
- Incorrect assembly, such as flipping the fan direction, can agitate particles rather than filtering them
- Performance depends heavily on using high-quality MERV 13 or 14 filters
- Requires manual assembly and periodic filter replacement using duct tape or cardboard shrouds
Best for
- Large rooms or open-plan living areas
- Budget-conscious air filtration
- High-dust environments like workshops
- DIY enthusiasts comfortable with basic assembly
Avoid if
- Aesthetics and home decor are a high priority
- You have very limited floor space
- You require a near-silent device for a bedroom (unless building a specific PC-fan variant)
This summary uses balanced time weighting with about a 6-month half-life. The evidence is older, with a median source age of approximately 297 days, though the DIY nature of the product makes these insights relatively stable.
Sentiment
82 positive (82%) · 14 mixed (14%) · 4 negative (4%)
Trust + time weighted score: +79% · raw score 78%
What redditors said (10 of 100)
I learned of a Corsi Rosenthal box (using MERV 14 filters) and decided to build one, but in my haste, I flipped the fan to be blowing air into the center of the box instead of upwards and let it run all night. My best guess is that the incorrectly built Corsi Rosenthal box ended up agitating the particles in our room and we inhaled some while sleeping.
Another good choice is building a CR box. The high setting will definitely be too loud, but this site found a decibel reading of 49 on the low setting
Levoit Vital 200s or Corsi Rosenthal Box
you get an Air purifier called a CR Box/Corsi Rosenthal Box...that does a whopping 440 CFM of air cleaning power. Better than any sub 400 dollar purifier, and better than some 1,000 dollar purifiers...for 90 bucks.
a CR Box/Corsi Rosenthal Box a great way to get cheap particulate coverage. (A CR Box only 90 bucks..and 440CFM power...so will be like 4x more powerful than that Coway...for same price.
Good news is a cheap option is a Corsi Rosenthal box, which you can make yourself...for about 90 bucks. You simply buy a 30 dollar box fan and tape 4 merv 14+ filters around it preferably. This is energy efficient, light weight wtc. And will move a whopping 440CFM of air on high.
This generates a whopping 400CFM for only 90 bucks. Better than any sub 400 dollar purifier. ... I second the CRbox as an inexpensive and highly effective air filter
Just build your own out corsi rosenthal box they’re way better than any store bought air filter and they’re miles cheaper
In most cases a simple box fan with a filter will be cheaper and out perform most of these devices. https://corsirosenthalfoundation.org/instructions/
Make a Corsi Rosenthal Box with a fan and 4 HVAC filters. Cheap af and extremely effective
Compare
Corsi-Rosenthal box vs Levoit Vital 200SCorsi-Rosenthal box vs Levoit Core 600SCorsi-Rosenthal box vs AirFanta 3 Pro
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