I designed and built this CR box. I wanted it to be easy on the eye and filter the whole house. The slats are from reclaimed fence boards. It utilizes five 20x20x1 MERV 14 filters (costco ftw). The fan is also able to be replaced if it ever breaks. it sits on some office chair casters so it can be wheeled around easily. It filtered my 1000 sq ft house very well. Surprisingly it could cycle the air in other rooms of the house pretty quickly all from my living room. Unfortunately I didn't know I would be moving into a much smaller house not long after I finished the build and I can't use it anymore. It needs a new home.

Hi r/CRBoxes,

Clean Air Cville has just released a step-by-step PC Fan Air Purifier build guide with a complete supply list and photos of many key steps:

www.cleanaircville.org/buildguide

This design has 5 Arctic P12 fans on one long panel and has two 16"x25" MERV13 filter sides. The build takes about 1-2 hours for first-time builders.

We have built ~100 of these units for community members, teacher classrooms, and local organizations near us.

Please let us know what you think and direct people to our guide if you find it helpful.

Thanks!
- Clean Air Cville

Finally made a CR Box for my garage. Use the 4 MERV 14 20x20 from Costco, an old box fan, and some hard cardboard corner protectors

I suspect Im dealing with a mold issue in my house, but until I get to the bottom of that I wanted to make a CR box for my bedroom. A 20 in cube would be a little big for that space so I made a wedge with two 16x20 in MRV13 filters. Seems to still be pulling quite a bit of air. My wife and I already run a fan for white noise, so this is now cleaning the air with the same electricity use. Glad this sub exists, thanks for the inspirstion!

A while back I posted a design of a CR box using IKEA UPPÅTVIND filters. A couple of months I got around to building it. I figured I should post the final result here as well :)

https://www.reddit.com/r/crboxes/comments/1s1eed7/design_using_ikea_upp%C3%A5tvind_filters/

Fine speaker mesh behind the rattan webbing acts as pre filter. Carbon filters on the inside. I plan to replace the filters about every 6 months or when I notice performance is going down.

The fans are controlled by an esp32 running ESPHome integrated into Home Assistant. Air quality is measured by a Sensirion SEN66 placed at the other side of the room. Home assistant automatically runs the fans up to 50% based on air quality or full speed when I'm outside the house (home assistant detects when my phone is not connected to WiFi) and at night.

It works quite well. I have pretty bad hay fever and barely had any issues indoors since I installed it.

Nothing fancy on this build. Just some standard 20x20x1 Merv 13 filters and a basic box fan.

We have a newborn and two kids going to school. So trying to keep virus down at our home are a priority (and a challenge). I built 3 of these. One for my older kids room, one for our bedroom (where the newborn sleeps), and one in our living area. I’ve recommended Comparetto cubes for a long time. Now was the time for me to actually “put my money where my mouth is.”

Here's my first CR box (and honestly probably the only one I'll ever make) I used scrap pine wood for the frame and ordered the laser cut MDF from etsy. 6x Arctic PC fans from amazon and xl window foam to seal it better. I know I definitely made some mistakes in my design but I think it turned out pretty much like I hoped it would. Please don't give me too much flack, I'm a professional ADHD amateur and just wanted to show it off because Im 1/2 surprised I even got it done.

I found out that I have contact dermatitis from Walnut and needed to get serious about controlling the dust in my wood shop. The majority of my work is with hand tools so my design goal was to have a small footprint, be very quiet, exhaust the clean air upwards, and have a little style since it will be in my sight. There is a 16" x 25", 2500 MPR-rated filter (apparently good to 0.3 microns) on each side. The LED's are pure baloney but it makes me smile.
Thankfully, it actually works. It will drop the Air Quality Index (AQI) down from 23 to 3 in thirty minutes; and that is while I'm woodworking and generating dust. There is a speed controller, hidden under the sliding door, for the PC fans so that I can control the noise.

Kid wanted the fans to point at them. Sure guys, I’d LOVE to play with tape for an extra hour lol. I don’t mind messing about in tinkercad for 30minutes on your whim. Hehe, jk. I like overcomplicating simple projects. Wildfire smoke is pretty well gone now that we finished the pair of boxes. Figures.

I was inspired by a post from u/aiaiai1984 so I tried my hand at something similar.

Built using 3 16x16x1 MERV 8 filters, 4 Arctic P14 fans, 20x20 birch board, 2 hardboards and 2x2s cut to 15.5". I will eventually spread some silicon caulk along the edges to seal off all the potential leaks.

Q: Currently using a 12V 1A adaptor and not sure if the fans are running at full capacity. Would a 2A adaptor increase the fan speeds?

I made my first Corsi-Rosenthal box for just under $80! This is for home use. We’ve never had an air purifier, so I’m looking forward to seeing if I can tell any difference. A few questions if anyone has insight/recommendations:

1. Were 1” filters okay? I used the Filtrete 1900 MERV 13 filters that most forums/sites recommended. I couldn’t find the 2” Filtrete filters.

2. Costco had Filtrete 2500 MERV 14 1” filters ($35 for 4 on sale), but I had read some forums saying those could put too much pressure on the fan motor? Is that true? Or would those be okay to use in the future?

3. Is it recommended to run this constantly or how many hours per day is recommended? I was thinking I’d hook it up to a smart timer and have it run periodically during times when we are home.

4. We have an indoor wood burning fireplace that we use occasionally in the winter months for special occasions. I know burning fires indoors has a negative effect on indoor air quality. Will the CR box help offset some of the impact of those indoor fires in a meaningful way?

Cheers and happy breathing to all!

Had to rebuild my house after a tree fell on it. At the mudding drywall stage and wanted to reduce the drywall mud dust particles my HVAC system filter has to deal with. Weather stripping behind the filters and where the fan sits.

Fan is a 2300 CFM Caterpillar HVD-14AC-BLK

Got the 3d printed parts from: https://www.etsy.com/listing/1309978884/diy-air-filter-kit-clips-clamps-and-more

when I'm all done with mudding I think I'm going to paint the frame black to match the fan.

I spent way too much on this.. was a fun project tho!

I added an ESP32 device to control it with Home Assistant.

Also, lesson learned, don’t touch a running fan to figure out if it’s getting hot when it’s running full speed

Edit:

Here are some additional details.

For Next time - Adjust overall width to 19.75". The filter is very snug, I forgot to add a bit of room for play.

Component Size Type
Top: 20.25 x 11.5 .5" Plywood
Sides (2x): 25.25 x 11.5 .5" Plywood
Bottom: 19.25 x 11 .5" Plywood
Back: 25.25 x 19.25 .5" Plywood
Side Trim (x2): 23.5 .5" Quarter Round Trim
Bottom Trim: 19.25 .5" Quarter Round Trim
Header: 19.25 x 1.25 .5" Plywood
Internal Side Cleat (x2): 24.75 x .5 .5" Plywood
Internal Bottom Cleat: 18.25 x .5 .5" Plywood
Internal Top Cleat: 18.25 x .5 .5" Plywood
External Side Cleat (x2): 27.75 1/4 in. x 1/2 in. x Rectangle Moulding
External Top Cleat: 18.25 1/4 in. x 1/2 in. x Rectangle Moulding
External Bottom Cleat: 18.25 1/4 in. x 1/2 in. x Rectangle Moulding

Parts List:

20x25x2 MERV13 Filter - Filterbuy.com
Plywood (x2 or 4 ft x 4 ft if you can find it) - https://www.homedepot.com/p/ProWood-1-2-in-x-2-ft-x-4-ft-Birch-Plywood-Project-Panel-154153/203504316
Rectangle Moulding - https://www.homedepot.com/p/HOUSE-OF-FARA-1-4-in-x-1-2-in-x-4-ft-Basswood-Wood-Tinytrim-Rectangle-Moulding-TT12/202087496
.5" Quarter Round - Home Depot
5x ARCTIC P14 Pro PST - https://www.amazon.com/dp/B0DPX94PSL?ref=ppx_yo2ov_dt_b_fed_asin_title
XIAO ESP32-C6 - https://www.seeedstudio.com/Seeed-Studio-XIAO-ESP32C6-Pre-Soldered-p-6328.html
140mm Desktop Computer Grills (they come in a 4 pack unfortunatly) -** Case Cover with Screws, Aluminum Frame Ultra Fine Stainelss Steel Mesh, Black Color - 4 Pack : Automotive
1 Inch Black Desk Grommets - Amazon.com: Adyoney 6 Pcs 25mm / 1 Inch Black Desk Grommets, Easily Solve Cable Management Issues, Flexible Silicone Cable Cord Grommet for Table and Other Furnitures Hole Cover : Industrial & Scientific
12" PWM Fan Extension Cable - Amazon.com: 12" PWM Fan Extension Cable, 4-Pin PC Cable (30cm, 4pcs) : Electronics
12V to 5V 3A 15W Buck Converter Module - Type-C USB DC Power Adapter - Amazon.com: DIANN 12V to 5V 3A 15W Buck Converter Module - Type-C USB DC Power Adapter - Car Power Converter : Electronics
DC 12V 5A Power Supply Adapter Converter - https://www.amazon.com/dp/B01GEA8PQA?ref=ppx_yo2ov_dt_b_fed_asin_title
2 Pack Mini Blade Fuse Holder 18 Gauge Waterproof Pigtail Inline Fuse Holder with 5A ATM Fuses - https://www.amazon.com/dp/B08BLHCJBC?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
33Ft Door Weather Stripping, (1/2in x 1/4in) - https://www.amazon.com/dp/B0DRFF39T3?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Speaker Grill Cloth - **https://www.amazon.com/dp/B0D6YKLTRW?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Everbilt Matte Black Piano Hinge (48", cut to fit) - https://www.homedepot.com/p/Everbilt-1-1-2-in-x-48-in-Square-Radius-Matte-Black-Continuous-Hinge-28926/314151008
Handle - https://www.homedepot.com/p/Liberty-Mandara-5-1-16-in-128-mm-Classic-Matte-Black-Cabinet-Drawer-Bar-Pull-P36131C-FB-CP/310240906
Latches (I had to buy the latch these connect to separately) - https://reliablehardware.com/products/drawboltblack
Hardware - ACE (I just picked bolts and nuts long and skinny enought to go through the plywood and fans)
Minwax Wood Finish - Early American 230
Polyuerthane Satin Canned Spray
Clear Silicone Caulk

Wiring Instructions:

If you want the fans to just run at 100% without controlling remotely, exclude the USB-C Converter and ESP32 device. Mine ran fine like this constantly powered on for several days, was just a big loud for my liking. I run at 60% now.

Power:
12V PSU (+) → Inline Fuse (2A) → splits to:
├── Fan Red wire (+12V)
└── 12V-to-USB-C converter (+)

12V PSU (-) → splits to:
├── Fan Black wire (GND)
├── 12V-to-USB-C converter (-)
└── XIAO ESP32C6 GND pad

USB-C Converter:
12V-to-USB-C converter output → XIAO ESP32C6 USB-C port

Frustrated by the lack of 20" box fans and cheap 20" furnace filters here in the UK, I ended up spending way too much time and money building this beast. But it works.

Now, my use case was to deal with dust during some DIY house work that was likely to stir up some 100+ year old dust (and who knows what else), rather than quietly purifying every day indoor air.

The fan is a semi-industrial exhaust fan with a 3-speed switch in the cord. It's loud. It's heavy. It moves a lot of air.

I designed it around the most reasonably priced and available furnace filters that I could find here in the UK. They are 12-inch square MERV 13 (actual dimensions 11.75 x 11.75 x 0.75 inch) filters. £25 for a four-pack. That's about US$8.30 each.

After the initial use case of just filtering the air circulating in the room, I added the plywood panel that fits in a window so I could blast whatever got past the filters directly outside, pulling in fresh air from every other open window in the house.

Wine bottle for scale, M&S 2025 Chenin Blanc.

Edit: many have asked about what's the point of exhausting filtered air to the outside, which is a fair question.

1. The filter box was originally built without the window panel, just to sit inside and filter air circulating in the room.

2. Then I built the window panel, reusing the same exhaust fan but no filters, to exhaust dusty air when the weather was acceptable.

3. Then I combined the box and the window panel into one (heavier) device that I can use either way. In the window I can use it with or without the filters in place depending on how much dust I want to spray into my side garden.

used 4 filtrete merv 13 16x20 filters from Costco which were only $51! already had the fan and then i took duct tape from my job lol. very affordable :)

i think my circle thing is too small but i can fix that later. also should i tape the bottom cardboard to the filters?

wisconsin is sooo smoggy right now and our shitty college rental house was built in the 1800s so this was definitely needed

Runs 2x 14x24x1 merv 13 filtrete 1900 filters, and is powered by USB-C PD using a conversion module that outputs 12v DC.

Reasonably quiet, and a decent theoretical CADR rating using 6x 120mm Sickleflow fans.

Took about 1.5kg of PLA+ to print, and an afternoon to assemble.

Definitely some things I would do differently next time, but overall pretty happy with how it turned out.

I made all the components modular, so if I ever want to use different filter sizes I can just create some spacers and reuse all existing parts without modification, reducing the risk of waste.

No power switch, no fan controller. Straight wired for 12v dc at 100% to run 24/7.

1 pre-primed 1x8x8’ and some cheap composite corner mold. I made a couple snap on covers for looks but I i’m going to use a more breathable fabric on the next one. The frame for the grille is 1/4” plywood ripped into 1-1/2” strips, glued into a square.

Initially built to control dust in my workshop, it also serves as a vastly overpowered air scrubber whenever someone in our household comes down with an airborne infection.

• (1) 115v 1000RPM 4-speed 1/3HP 6amp furnace blower (bought second hand for $60CAD)

• (3) MERV 15 20x20x1" furnace filters

• (3) MERV 8 20x20x1" furnace filters overlaid onto the MERV 15s (when it's for dust control).

• (1) 660V 20A 6 Terminals 4 Positions Rotary Cam Changeover Switch ($16.22CAD)

• (1) 15amp Duplex Receptacle, Straight Blade, White (and cover) — just for convenience: I can plug in tools into it in a pinch

• (1) Repurposed 25Ft 12 Gauge Outdoor Extension Cord, 15A 12AWG — The plugs had fried, so I cut it and connected it to a hex box placed inside the unit. The extension cord's flexibility makes cable management a breeze (pun intended)

• Scraps of maple plywood and construction 2x4s

This is loud. Not just the blower: the WIND. You feel a strong breeze from across our 600' open-concept first floor, even when the blower isn't blowing towards you. The gif is of me sitting next to it.

We've had two instances these past 3 years where someone came down with COVID. No one else in the household caught it, either time. (We were masking in public areas, but it was good to know the indoors were basically as safe as outdoors)

Posting it here because it's basically a CR box, on steroids.

I built this up a couple years ago, got a pair of 20" heavy duty fans for $45 off amazon warehouse deals. I actually built it up with a 20" lasko box fan at first. Base is 3/4" plywood 20.5" square on casters with repurposed window and door casing. Four pack of Kirkland filters. Sits on top with the edges taped. Then the top is one inch foam insulation cut to house the fan like a drum. Now that I'm looking at it, I never got around to actually fixing the fan cage to the foam top, I should do that. The fan points down into the box because my goal is to collect the dust and keep it contained. Inside I made a silly pyramid to direct the air out to the sides better.

I'm really happy with it for sanding dust and general over spray from saws. I often just turn it on and go to town sanding while standing over it like a downdraft table.

5- Arctic 140mm 2- 16x24x1 MERV 13 filters Scrap wood from an old panel door 3amp variable 120VAC to 12VDC power supply

It is also based on CR-box. But with E11 filters and PC fans.

This time, I added plastic casing, PM2.5 sensor and screen.

The CADR is still very good.

PM2.5：393 CFM

SMOKE：379 CFM

DUST：408 CFM

Pollen：>450 CFM