DIY Portable Air Filter

A Corsi-Rosenthal box is a very simple and inexpensive DIY portable air filter that became popular during the pandemic, but the concept has been around a long time. They can be a good alternative to more expensive/proprietary portable HEPA filter units (also commonly known as ‘air purifiers’).

Making your own Corsi-Rosenthal air filter is pretty simple (a little kid could do it) and replacement filters are relatively inexpensive.

See Wikipedia for more basic info and search online for design options.

Also see my other blogs on indoor air quality and residential HVAC ventilation units.

Podcast

My Air Filter Design

The basic version I made, after reading the Corsi Foundation’s guide and watching this video and others:

Four 20″x20″x1″ 3M Filtrete 1500 filters (MERV 12). I got two 2 packs at around $30/pack. Then later I saw much higher rated Filtrete’s in a 4 pack at Costco for much less. Oh well. Shop around! NordicPure 2″ thick filters with higher MERV ratings are also common.
20″ Lasko fan (these are just over $20)
White duct tape (I also hear gaffer’s tape works well)

I think the total cost was around $85. Replacement costs will depend on how much we run the filter and how much I’m able to keep up with house cleaning ;)

You use the fan’s box for the 20″x20″ base and then the other large piece for a “shroud” for the top. My top shroud has a 15″ circle cut in it, which is supposed to work well for Lasko fans—this could vary a bit based on what fan you use. The shroud helps direct the airflow straight upwards and makes it more efficient.

I’ve been using the Corsi-Rosenthal box in my office on the low setting during the day and in our main room on high at night. It should really cut down on the dust and pollen in our Tucson, AZ home.

If you want to rock out to a cover of my old punk band’s song (including a version of my one and only recorded guitar solo) and see some simple instructions watch this video!

Update: Filter Changes Are Easy!

I used my box for months and started to notice a slight dusty smell coming from it. The filters had done their job and needed replacing. Costco had a great deal: $38 for four MERV14 filters. It was very easy to cut the tape and add the new filters! Here’s what it looked like (looking from bottom of box before I put the cardboard piece back on):

More Advanced Designs

This YouTube search has endless videos to wade through.

People have begun creating versions with computer fans to decrease noise and many other creative ideas are being shared. Some of the more advanced designs are starting to look quite slick and some people are selling build kits online.

People are using thicker filters, different sized filters or non-box configurations, more filters (5 vs 4), higher rated filters, other better fans, pretty much anything you can think up.

This video has a cool review of many different types of filters, and was the reason I went with simple 3M filters for my first build:

Questions?

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