Corsi-Rosenthal Boxes

Options and sources

CR box air filters are powerful, inexpensive, and some are super quiet. And they can go in a classroom or business or home right away, adding filtration capacity ASAP, even if your school district or landlord or HVAC system is not ready to provide sufficient ventilation to make your indoor air safe.

Our favorites we recommend and have experience with are the CleanAirKits.com Tower of Power, the Owl Air, the traditional CR box using a box fan, and the Elfstrom single fan filter. All of these options can be DIY’d, and some can also be purchased if you are short on time to commit to doing your own build.

Easy mode – CR boxes you can buy

Owl Air

There are currently stalled efforts to develop the Owl Air LLC, with a goal of making it available for sale.  Interest in purchasing might revive the effort. If you’d rather buy an Owl Air than make one, please reach out to info@safeairoregon.org so that we can pass along interest to the Owl Air LLC folks.

Tower of Power

Two options are available from CleanAirKits.com:

Option 1: STEM Kit

Total price: $270

  • Blending easy mode of purchasing with the fun of doing a DIY build
  • The STEM kit includes parts for assembling the fans into a sturdier, and more easily reusable, frame than our current DIY build — the cost for all the parts you need to build the frame is ~$225 ($209 + shipping)
  • 2 3M 20×30 MERV 13 filters need to be bought separately – $45 for 2 filters at Amazon or Lowes, or stock up and buy 4 for $72 at Lowes.com
  • Total for one STEM Kit version: $270
  • Purchase the frame parts here selecting “DIY STEM kit” and the filters here

Option 2: Pre-assembled with filters

Total price: $340 — not currently available

  • Super easy mode! This is fully ready to go out of the box. Cost is $289 + ~$55 for shipping.
  • Total for pre-assembled version: ~$340
  • Purchase both the fame and filters all ready to go here

Save money mode – CR boxes you can build

DIY Owl Air CR box

Total price: ~$160 – $175

Warning: This build is dependent on the Honeywell HF-910 fan, but the HF-910 seems to go in and out of being in stock or not. Some of our members have been told that it goes in and out of availability because it is a seasonal item, while others have been told that Honeywell is discontinuing this fan. Fingers crossed it remains available!

Tools and materials needed Recommended sources + typical price
Honeywell HF-910 + the box the fan comes inWhen in stock, Staples & Walmart have given free shipping – $57
4 MERV 13 furnace filters
Size: Either get 20” x 20”, 20” x 25” or 20” x 30” filters

We are also experimenting with a build that uses 24″ x 30″ filters
We may recommend this size in the future
3M Filtrete

Amazon
Get a 4-pack of 20×20 or 20×25: $92 ($23 each)
or
Get 2 2-packs of 20×30: $90
or
Build three CR boxes with 2 6-packs of 20×20: $250 ($20.85 ea/$83 per 4 filters)

Lowes.com **Best deal ($18.40/filter) + delivery is free & quick
Get 4 filters (any size): $74
(Lowes discount off of $92 if you buy 4 filters at once: 20%)
                                   
Tape + covering materials
Recommendation: Gaffer’s tape in two sizes (2” and 4”)

If you prefer, you can also use duct tape, or duct tape and contact paper
But we’ve found Gaffer’s tape to be the easiest to work with
Amazon

Get 1 roll of 2-inch black Gaffer’s tape: $20
You can also bring the cost of a roll down to $9 with 4- and 6-packs

And

Get a 2 pack of 4-inch white Gaffer’s tape: $21
A 2-pack will cover multiple Owl Air box tops
Weather stripping & glue (optional)3/16” weather stripping ~ $3
Scissors, measuring tapeN/A

DIY Tower of Power CR box

Total price: ~$175 – $250

Tools and materials neededRecommended sources + typical price
10 Arctic P14 PWM PST PC fans

Note:
The Arctic P14 and the Arctic P14 PWM PST are two different versions of this fan
The PWM PST option is ready to plug together and has worked well
Amazon
2 5-packs – $50 per 5-pack – $100 total
2 MERV 13 furnace filters
Size: 20” x 30” filters
3M Filtrete

Amazon
1 2-packs of 20×30: $45 ($22.50 ea)

Lowes.com
4 20×30 filters: $74
(Lowes discount off of $92 if you buy 4 filters at once: 20%)
Tape

Recommendation:
2” Gaffer’s tape

You can also use duct tape, but we’ve found Gaffer’s tape to be the easiest to work with
Amazon

1 roll of 2-inch black Gaffer’s tape: $20
(You can bring the cost of a roll down to $9 with 4- and 6-packs)
Thick foam posterboardMichael’s

2 – 20×30″ Core Foam Boards – $8 ea – $16 total

If making 2 CR boxes, get 3 – $24 total
Power adaptorsAmazon

Get DC power supply Chanzon 12V 2A 24W Class 2 Power Supply AC DC Switching Adapter – $15

and

Get fan power adapter cable CRJ Female DC Power Supply Plug to PC 3/4-Pin Fan  Power Adapter Cable
$5.50 for 1
2-pack for $7.99 – if making 2 CR boxes
Hardware & screening (or fan grilles)

*Ask if we have extra hardware & screening to give to your build
Get hardware: 40 45mm M4 bolts, washers, nuts – $34 for 100 of each (covers 2.5 boxes)

and

Get screening: Plastic chicken wire mesh – $15
(covers multiple boxes)

or

Alternative to screening: 10 PC fan grills – $12
Box cutter, glue, templateBorrow our template or get large thick paper to DIY

Traditional DIY CR box with box fan

Pics by twitter.com/gf_traveller, encycla.com/Corsi-Rosenthal_Cube, en.wikipedia.org/wiki/File:Corsi-Rosenthal_Box.jpg, CC BY-SA

Total price: ~$100 – $130

Tools and materials neededRecommended sources + typical price
20 inch box fan
+ keep the box for making the optional but flow-enhancing shroud
Lasko or Utilitech – $30
4 MERV 13 furnace filters
Size: Either get 20” x 20”, 20” x 25” or 20” x 30” filters
3M Filtrete

Lowes.com
4 filters (any size): $74
(Lowes discount off of $92 if you buy 4 filters at once: 20%)
Tape + covering materials

Recommendation:
Gaffer’s and duct tape

If you prefer, you can use just duct tape, or duct tape and contact paper
Amazon

1 roll of 2-inch Gaffer’s tape: $20
You can bring the cost of a roll down to $9 with 4- and 6-packs

2 pack of 4-inch white Gaffer’s tape: $21
These 2 packs will cover multiple shrouds

1 roll of duct tape: $9

                    

Elfstrom single filter fan CR box / SAFE Box

Total price: ~$60 – $80

Tools and materials neededRecommended sources + typical price
20 inch box fan
+ you need the box
Lasko or Utilitech – $30
1 20×20” MERV 13 furnace filter3M Filtrete – $23 each at Amazon or Lowes.com

Or get 4 filters for making 4 CR boxes – $74 from Lowes.com – best deal at $18.50/filter
(Lowes discount off of $92 if you buy 4 filters at once: 20%)
Tape + covering materials

Recommendation:
Gaffer’s and duct tape
Amazon

2 pack of 4-inch white Gaffer’s tape: $21
These 2 packs will cover multiple Elfstrom boxes

1 roll of duct tape: $9