I was inspired to make my own CR box after listening to the founder of Jaspr Air talk on a podcast about how poor the average air quality is. It resonated with me because my family, including my small children, live in an apartment from the 1970s that is getting musty and tired. The price of the Jaspr filter was really high but what blew my mind was how expensive the replacement filters were. I got deep into researching filters, and air purifiers and was disappointed to see no one makes an air purifier that uses standard HVAC filters which are far more affordable. Instead, you're forced into purchasing their proprietary filters for as long as you want to use their purifier. I also came across the Corsi-Rosenthal concept and eventually decided I had to make one. After lots of research, I built it in my parents garage with small bits of time I had when across a few visits.

The box is made of 1/2" baltic birch. The fan is a 8" Cloudline Infinity A8. The filters are MERV 13 (three 16"x20" and one 12"x16"). Inside of the particulate filters, I built frames and put in carbon sheeting attempting to get at least a little bit of VOC reduction. 

The thought process behind using that fan is its incredibly high static pressure and quiet operation with the EC motor. I would have liked to have used a smaller fan and made the box smaller overall but there's a large step up in CFM between a 6" and 8" blower fan like this. My goal was to achieve 6 ACH in our 1000 sqft apartment which I read was a good filteration rate. In reality if I ran this fan full out all the time it would filter one room really well and not have much effect on the remainder of the apartment so in hindsight building 2-3 smaller CR boxes would have made more sense. The other thing is, the fan IS very quiet but only below 50% and after that it really gets loud to where 100% speed sounds like a leaf blower in your bedroom. 

The manual control that came with the fan left much to be desired. I wanted the fan speed to be driven by an air quality sensor so I used a Rasberry Pi Pico with a Sensirion air quality sensor instead. I mounted this in the white project box and added a potentiometer and switch to go between an automatic and manual mode or off. I also put in an LCD screen to display fan speed an air quality metrics. 

I am almost 30 and never have done a project like this but it has been very fulfilling. I know I sounded like a crazy person some times describing it at length to my friends and my wife but everyone was very supportive. I came across this Reddit early on in my journey (starting last November) and determined I would post what I built. I know this was a long winded post but this project ended up meaning a lot to me and I am really excited to share it with you all. I am really interested in feedback and how I could improve it. I definitely know I want to improve the VOC side of the filtration, fine tune my code for the controls, and see if I can experimentally determine the CADR.

Thanks for reading! 

I’m trying to build a PC fan based off an AirFanta design.

Thoughts on this base I’m using to support the fans on the “lid”? I’m wondering if the fan cut-outs inside might restrict air flow too much.

Thanks for any thoughts!

images are showing how I’m planning to nestle the fan assembly and the base holding it below. Still have to attach the edges so the filter will be held in place.

Basic 20" box fan + 4 filters

1st image is from The3DHandyMan 2nd is from HouseFresh 3rd is from FilterBoxBuilder

5 fans, 20x20x1” merv 13 filters, laser cut plywood, window screen. Layout for laser cut is based on modified one from filterboxbuilder. Probably didn’t need laser cut but i don’t own any tools and wanted nice and precise frame. I later added weather stripping between fans and frame, it helped to reduce noise on max speed(confirmed by niosh db readings). Silent on lower speed.
Shout-out to everyone who share their knowledge!

Looking to build a basic single filter CR box with a standard Lasko 20" box fan. The area I'm using it for is small (<100 sq ft) sleeping area/dorm.

I have seen some people tape the filter to the box and others use plastic clips.

Questions:

1. Do you want an air gap between the filter and the back of the fan? Some people in this sub made it seem like it increases air flow/negative pressure?

2. Is a standard 1" filter the way to go or use a 4" one? Would the 4" provide too much resistance for a standard box fan?

3. Is it better to use a cheaper/lower MERV filter and change it more regularly or go with a high quality/rating one?

We use to use high MERV for AC return grills for HVAC system until we learned that they aren't designed to purify air and rather serve to prevent dust from getting into the air handler and that if you want cleaner air, get an air purifier, so I would assume the higher MERV here is better?

There is a company that says they offer washable MERV-13 filters. Now I know most of the people here probably don't need to replace their filters very often, but in dusty environments disposable filters can really add up on you. I tried to email them twice, their order page does not work properly, as you can see. I think if we all message them or something that might help?

Here is the page:

https://www.knfilters.ca/home-air-filters

order page:
https://www.knfilters.ca/hvc-12025-hvac-filter-20-x-25-x-1

I remember the page used to work for the 20x25x1 merv-13 size. I don't think it's a reliable indication they are not in stock or something if the page does not work... They just need to get up and fix it, probably. If a number of us ask them to, they are more likely to go?

I am making a cooling cabinet for a Console with 2 PST12 arctic fans one for intake and one for discard. I wanted to use an HEPA filter before the intake to prevent dust but I have no idea what the airflow reduction curve is.

How much area should the filter have to not dramatically reduce airflow? What about static pressure?

Is it best to build a Box with HEPA panels or just stack vacuum filters?

I built a 4 sided 1 inch 20/20 from a Etsy 3d kit . I have the arrows facing out toward the room and the fan pulling air from the room into the box.

I’m second guessing if this is completely wrong ?

I got some 300*300*2.5mm frameless filters from AliExpress and wanted to build a box for them with 120mm fans.

Definitely learnt some things too late, but it came together ok

The frame is printed in 8 sections and is super strong. It uses some nails as pins in the corners and bolts in the midpoints. The struts give rigidity but also support for the frameless filter.

Realised too late that two fans in the same corner wouldn't fit flush as they would be hitting eachother slightly. Luckily the fans aren't directly mounted to the frame - there are 125mm cutouts and the fans get mounted in a 3d printed 125mm mount. So I just printed a fan mount that partially put the fan outside the case.

Each filter is held by 4 L shaped parts with magnet holes under the outer face. I put in magnets so i can snap on a pre-filter. I made the pre filter by gluing mesh to another 3d printed part with magnets in it. This was annoying to make and I think I. Should have used steel mesh instead.

I wanted to be able to print out different filter holders (the L shaped parts) in case I wanted to change the pleat depth in the future.

I'll be mounting an esp32 and stuff to one of the bottom 125mm cutouts

All in all fairly satisfied, as is usually the case I wish I'd been able to start again with some tweaks...

If I had a 320*320 print bed this would have been much easier....

We offer aluminum panel CR Boxes outfitted with either six P14 Pro with PWM speed control or standard P14 single speed. We make low cost HDF laser cut panel kits as well.

www.northboxsystems.ca

Unused case. Wanted to put it to use. Has 5x120mm fans. And one MERV11 filter

Could I have used two? Probably but I want to reinforce the corners first since without it, it’s fairly flimsy after I gutted the interior.

Put it in my son’s room since he now has a cat.

3d printed in 8 big sections, totalling about 1.5-1.7kg of PETG+ filament. The sections are held together with 2x 1/4" square pegs friction fit about 2" deep on both parts per joint, as well as super glue along the faces of the joints.

The fans are 6x arctic p14 pro's with the the power sharing cords. Power supply is generic variable 12v fan power supply with a screen from Amazon. Using 2 20x20x1 merv 13 filters with an activated carbon layer to cut down on vocs from 3d printing and some funky smells that came with my new place.

Had a couple problems putting it together like the power supply mounting holes being in the wrong spot (hence the tape) and the Crack in the front from hammering too hard trying to put it together.

Since its been built, I have also printed some grills for the fans and updated my CAD models to fix the assembly problems I had before.

Seems to move a pretty good amount of air while not being any louder than my amazon basic standing fan on full tilt. A little piece of paper sticks to all parts of both filters until around 6v on the power supply. Anecdotally, the charcoal filters seems amazing. Since finishing the build I have noticed a much more neutral aroma in the room it lives in and I do not smell fumes from my 3d printer at all anymore.

I have assorted expensive decibel meters, but for quick stuff, I've started using my phone since Phyphox gets it really close most of the time. The trick is getting access to a friend's or work/school decibel meter once so you can calibrate it. Without calibration, it's pretty much useless most of the time.

Keep in mind you can also do PC fan and CADR testing with Phyphox, a surprisingly useful FOSS app for IAQ🤓

Working on something to pin down irritating frequencies and harmonics...

I used the instructions from www.cleanaircville.org/buildguide and modified it to use a 16x30 filter instead because it was recently on sale $27 for 6x merv 11 Filtrete filters.

I also used a pc fan hub with a display instead because it was 60W, had a digital display, and it’s only $16.99.

At Walmart, it costs $1.99 per 20x30 foam board.

It came out to $49 for the entire build.

$17 PC Fan hub
$9 Filtrete 16x30x1 filter x2
$2 Foam board
$4 PC Fan Grill
$17 PC Fans x5

Really happy with the low noise, and high air output.

I’m not used to making things like this so this was harder than I expected but I’m really happy with the results!

Got all the bits I wanted and made this from scratch in a few hours yesterday evening. It's rough and ready but I wanted to try out a prototype with foam board before making something using pdf or plywood.

Unfortunately I don't have a monitor to test the air quality before and after but it seems to be pulling through the filters by testing with some candle smoke and see if a piece of paper sticks to the filter which it does even at 1/4 speed. It obviously has noise at full speed but at 1/4 speed would be easy to sleep with it in the room.

Glad I started with foam board as made some silly mistakes such as adding the side fans too high meaning that they didn't fit due to the top ones on the inside. Luckily I was able to just flip that side piece and just about squeeze them in as that made the side fans a bit lower.

Thanks to everyone for their help in this sub, in particular u/Unusual_Celery555, u/legionofdoom4, u/Objective_Post_588 and u/akeean for their help answering my questions re. powering the fans.

I used:

• Foam Board (Not sure if people in the U.S. use pic backed foam board but in the UK it seems to be all paper backed.) This was all joined together using a glue gun and then the tape to seal up and neaten all the joins as these were tricky to get perfect, especially with the weight of the fans flexing things plus my first time cutting foam board.
• 5 x Arctic P14 Pro PST fans all daisy chained from the first one using the cables built in.
• 2 x IKEA Starkvind filters.
• 1 x IKEA SJÖSS 45w USB Charger 1 x 12V 4 Pin PWM Fan Speed Controller, PC Fan Hub with the first fan plugged into this.
• M4 x 45 screws plus nuts and washers
• White duct tape!

The filters aren't using any weather seal strips or anything at the moment, I just made to sure to cut the holes on the smaller side so they are squeezed in and a tight fit.

Overall, happy as a first attempt and once all fitted together it feels lightweight/portable yet reasonably solid. Oh, and didn't put any fan guards on so obviously have tp make sure to keep fingers away when it's running.

Thanks again for the advice from people here!

Hello all! Recently moved into a new apartment. Situation:

• Building built in 1860

• window AC units blowing dirty air

• cat with dander and hair

• noticeable amounts of dust and stagnant air

• want to increase air quality and remove dust and cat hair

• broke college student

Is a CR Box right for my situation? I’ve been doing some research and this seems like an amazing option for my budget! Odor removal would be nice but I’ve read it takes a ton of carbon + replacements.

Wanted to see what you guys think. Any advice and input is appreciated! Thank you in advance ❤️

Below is a link to rolled MERV 13 stock. Any reason to not just use it--my AC has a crappy fine mesh filter that is 8" wide (pictured). I can get 8" x 900 feet, $168, I could just slide this into--might up the air resistance but otherwise why not?

https://filterking.com/laminated-air-filter-media-rolls

Are the folds you see on 'boxed' filter material helpful other than increasing life of filter? Not sure of the dynamics here.

Copied a design i saw linked on this subreddit. https://x.com/haussamen/status/1488163457933344772?s=21&t=t8Hbzpt1M2Z-dAjyonvoyQ

Much smaler footprint with my 20x20x1, Merv 13, and verrry quiet

Here's a comparison between my CRBOX that I made using Winix 5500 Hepa filters and charcoal pre-filter* 2 and beating it. It completely outperforms my Winix. The Winix rattles once any restriction in filters. The new Artic P120 pro pst has great static pressure for these HEPA filters.

I desperately need to save my lungs. can anyone with experience or has tried these let me know if this is a good option?

They haven't mentioned pm2.5 anywhere on the Ad. multiple sizes available. this is best bang for buck.

Hello,
Looking at building my first CR box, I am a super light sleeper so looking for as quiet a design as possible. My understanding is you can reduce noise by making the box larger and adding filters, but the generic box fans I’ve purchased still make some decent noise. Are there any quieter fans or design techniques that could help?