DIY Air Purifier - 10 Minute Corsi–Rosenthal Box

If you're concerned or curious about air quality it's relatively likely that you've come across the Corsi-Rosenthal Box DIY air purification concept already. You may have even looked into or done some research on air quality monitors, which is itself a relatively "deep" pit of research, though I can highly recommend the PurpleAir air quality monitoring line -- more on air quality monitors below.

If you're in an area that is experiencing increased wildfire occurrence & severity, or if you're in a moderate-density city or suburban area, then you'll probably be interested in understanding, quantifying, and improving air quality already or in the near future. Monitoring your air quality is a great first step to understanding if you need to make improvements; if you do, especially if you need to make large improvements (wildfires, smog, etc) then the Corsi-Rosenthal box is a GREAT way to do so, without breaking the bank and while still getting commercial-level filtering capability!

Here's my (barely modified) "build" of a Corsi-Rosenthal box, including the "secret" to making one quickly & easily. :)

Hyper-local Quantifiable, 'High Efficiency' Improvments

I like to quantify & objectively measure everything, as much as I realistically can, and sometimes to a fault. I've always been interested in making small and often incremental improvements in my hyper-local environment, though with a strong focus on what I deem "high-efficiency" improvements. Essentially, that boils down to implementations/changes that have proportionately high-impact outcomes relative to the 'input' required to achieve that outcome.

In more concrete terms, my mindset generally boils down to the EV / value proposition -- for these kinds of projects it's generally along the lines of cost & labor inputs vs the quantifiable target outcome -- something along these lines if code representation makes more sense for you:


The 'Corsi–Rosenthal Box'

img This is what a 'standard' Corsi–Rosenthal Box looks like. The most common design is made up of: 1 box fan, 3 standard 20x20 HVAC high-MERV filters, cardboard, and tape. You can find numerous videos online showing how to put it together, including several videos from the original creators themselves. Several variations exist and the original creators have iterated based on lab tests in order to improve the efficacy & air-cleaning performance of the device. Generally, it's pretty straight-forward though - putting it together is relatively simple logic and even an 'imperfect' build will give you a functional outcome (air-purifyin device), though it may not be operating at the most optimal air-cleaning capacity. The most time-consuming aspect is "sealing" the box and it's not difficult by any means but it does require some patience and time. M

Most instructional videos estimate assembly time of 30-60 minutes.

Full disclosure: I'm not a big fan of meticulous taping - whether it be for a project such as this one or for painting, taping things is just not something that I enjoy.

10 Minute 'Corsi–Rosenthal Box' Build

Here's my semi-obvious take on putting together a Corsi-Rosenthal box -- rapidly, efficacious, and without the tedium of mass tape.

Parts List

  • Standard Box Fan - Qty 1 (~$25)
    • Higher CFM is better, the box should show CFM.
    • Amperage draw is displayed on the box and can be used to determine operating (electricity) cost.
    • Consider noise; you may wnat to run it on lower speeds when room is occupied for sound/volume reasons.
    • Skip 'smart' features; better off with a good AQ sensor + 'smart plug' + code to toggle based on AQI.
  • 20x20 HVAC Air Filter, MERV 13 or higher - Qty 4 (~$20/ea)
  • Cardboard, 20x20 - Qty 2 (free)]
    • Use the cardboard from the box that the fan comes in.
  • Tape - Duct Tape, Foil Tape, or Painter's Tape - Qty 1 (~$5)
    • We won't use much tape and you can get away with using none at all, but it's worth having some handy.


Hot Glue Gun!!

  • You will need around 5-10 glue sticks.
  • Glue Gun Recommentation:
    • I love my 18V Ryobi glue gun.
    • Extremely handy around the house & temporary 'tacking' while mounting.
    • You can find the Ryobi for $20-30, sometimes <$10 on DTO.
    • We have 2: my wife keeps one for crafts -- got them on sale, $10/ea via DTO!!
    • Heats rapidly, surprisingly high-temperature; uses standard size glue sticks.
    • I use the P305; I strongly prefer it over the 'compact' version.
    • Check DTO: Refurb P305 or Blemished P307 (dual-temp), or blemished P305.


Check out any of the videos online for assembly instructions. The beauty of the hot-glue gun approach is that you can lay down a "bead" -- similar to how you would with caulk -- and as long as your bead is of ample size & runs the entire length (height) of the filters, you will have an air-tight seal between the filters. You will go through ~6 (or more) glue-sticks but it's a trade-off that is well worth it, allowing you to assemble ~90% of the box in 2-3 minutes.

You'll still need to cut (and tape) some carboard for the shrowd, though you could potentially hot-glue the shrowd to the fan as well. The main part that you probably wont want to hot-glue is the 'gap filler' between the fan & the 'filter box'. While hot-glue is relatively easy to remove, yet plenty durable at creating an air seal, you will eventually want to replace your air filters & so you may want to use tape on that part to make fan removal easier for when the time comes to replace the filters.

Overall though, I was able to throw together a highly-functional and quite effective Corsi-Rosenthal box in about 10-minutes -- thanks to a simple glue gun!

Efficacy - Does it work?

What's awesome about the Cosi-Rosenthal box is that the device has been lab-tested and studied academically -- it works and is highly effective. I'll find and post citations when I have a chance but gist is that the setup generally performs as well as commercial-grade devices that cost >$1k -- meaning the value-proposition is really unparalelled.

Additional info to add in the future (TODO):

  • Add Citations / Links to studies
  • Add photos of my 10-minute Corsi-Rosenthal box
  • Write up my simple automation setup which uses PurpleAir to turn the box on/off