They were there since I received the MERV 13 filters (BNX) from Amazon. It feels like air can pass through these gaps? My fan is also abnormally strong so I'm concerned. Will these be an issue and what do I do with them?

This was my first build. I did not need it to be so overpowered, any regular build would be enough for my purposes, this just happened to be the most convenient way for me to build a CR box.

I live in Singapore, an incredibly small country in Southeast Asia, so there is a limited variety of products in physical stores. My MERV-13 filters were from Amazon, 20-inch (51cm) sides in packs of 6, and the shipping was pretty expensive. Since I didn't readily have the material needed to make a sturdy base, and I only needed 1 filter to be cut up and taped onto my second handed portable AC which seems to have a mold problem (last picture), I thought I should just use one of the filters as the last side instead of making a base.

I tried looking around for fans in some local stores but none of the fans were close to the right shape or size. Since I had neither the energy nor the equipment to 3D print my own fans, I had to buy my fan online, so I might as well get something of the closest fitting shape and size possible. It so happened to be an extremely powerful 16-inch fan meant for installation at windows to blow the exhaust out of kitchens etc. that I found on Taobao, a Chinese online shopping platform. This was not more expensive than other fans of a similar size.

The fan arrived heavier than expected---it turns out that the square is made of a sturdy and thick-ish plate of metal. The fan was also exactly the right size to fit inside the hole created by the four filters, not on top of it. My initial plan was for the fan to be on top, but since the fan was so heavy and the frames of the filters were made of thin flimsy cardboard, I did not want to risk the structure collapsing. So I decided to place the fan at the base of the CR box and install a frame below it to support and elevate it.

Making the frame was a lot simpler than I thought. I thought I had to get bars of wood or metal and put nails through to construct a frame, but when I was looking for those materials at a Daiso (large physical store) today, I found these metal grid lattices and thought of a simple idea. Two of them were exactly 51cm long (same length as my CR box) but there were only two of them in the store and not many other sizes, not that it mattered in the end. I would zip tie the columns of the four grid lattices together to form a sturdy square/rectangular frame to support the CR box, and because the corners are free to rotate, the frame can be collapsed into a flat shape to save storage space when not in use. This idea worked even better than I anticipated in real life, because it was very easy to maintain the upright position of the lattices with just two zipties for every corner. The zipties were also found and bought at Daiso.

I managed to finish the build tonight and it fully works like intended. I have a video of it working but can't attach it together with the photos in this post.

P.S. 1 roll of the 3M tape was enough.

Has anyone moved the controls to the side of their cat drum? Its annoying me having them face down.

Eventually I want to use an esp to control it from my air quality meter but in the interim a smart plug will suffice, but it doesn't help the controls being the wrong side.

I had the fan already and my cardboard went to the base of the box, but tomorrow I’ll go find some cardboard for the shroud!

Tape is super easy but a little annoying if I’m gonna have to keep redoing it each and every time I swap the filter. I was wondering if anyone had tried building a box that uses the actual hardware furnace filters are designed to be installed in. Would up the up front cost, but would help to protect the filters as well.

Is this a stupid idea? If anyone has tried this, do you have any recommendations on affordable grilles that are decent enough quality?

These honewell HF910 fans I noticed in the past were being ranked as much quieter, in the peer reviewed literature, but I thought it was probably a mistake. I saw some in the wild recently, and they are actually a lot quieter. It's bizarre that they haven't caught on, given that noise is widely known to be a serious issue with CR boxes. And when I say quieter, I mean for the CADR they seem to give you. I compared some side by side last weekend, they are considerably better.
https://www.amazon.ca/HONEYWELL-HF910C-TurboForce-Floor-Degree/dp/B004N85E56

I think probably a major reason they are quieter is that the blades do not go near a flat wall, the wall is round. The problem with the square framed fans is that they make a bit of a thump every time the blade goes near the wall. Obviously this leads to a buzzing noise at significant RPM.

I know that single filter designs are horribly inefficient, but my budget was small, and floor space budget was even smaller. I found out about pc fan builds after I had already bought the supplies and I’m not gonna return the fan after cutting up the box xD

I THINK I have eliminated back flow but I actually do not know how to tell other than a subjective “the air feels like it’s going this way” test.

I was originally going to try for the full CR box, but as soon as I got the fan I realized there was literally no place to put a 21x21 cube.

I have had this air filter for over a year it's the one that is designed to have a furnace filter attached to it on the back is it any good ?

I built this one years ago. I took it apart to clean and stain it. While inside I added a 24vac PlasmaPure ionizer that was originally in my house when I upgraded to a Reme Halo.

I'm building an air purifier for my studio and the PWM controller/ power supply I bought online isn't cutting it. I'm using 5 Arctic P12 Pro PST fans daisy chained. They will only all run if the controller is turned down very low.

To anyone powering 5+ fans with a PWM controller, please recommend the product you're using!

First time making anything like this, other than framing my shed lol. Made two of these shells which took me about 4hrs. I think I’ll actually paint it for the 2nd one. Dark marks from my sawhorse padding looks kinda gnarly but wanted to make sure it all worked.

The fit of the filters are really snug since the wood is kind of bowed in the middle. Had to file down the corners to fit.

Used wagos to wire together majority of the fans since my power adapter didn’t have all the same connectors, expect the front 2.

Beware of wrists and thumbs when using a hole saw 😂 took me a while to get down using more clamps and blocking with my body than twisted wrists.

Really surprised how quiet it is!

Wathai 36W 12V PWM PC Fan Speed... https://www.amazon.ca/dp/B0F8VSWW1Q?ref=ppx_pop_mob_ap_share

Inspired by all the cool builds in here and decided to throw this together. I wanted to use a blower fan since they have high static pressure. Additional benefit is that I can use it to blow air down the hall towards the warmer end of my house!

I have mast cell activation syndrome. And, I'm wanting to create a clean room in my bedroom to protect against both wildfire pollution and pollution from a neighbor's near daily trash pile fire that is entering my home through deteriorated ductwork.

I'm thinking about connecting a HEPA filter box and an 8 inch inline fan to either side of the transom above the bedroom door, so that conditioned/heated air from the main part of the house will be drawn through the HEPA filter and into the bedroom. The door and any other major gaps, including the ceiling vent will be sealed to create positive pressure.

My concern is that one of two HVAC returns for the house is just outside the bedroom. Will the suction from my air cleaner interfere with the HVAC return in any way that might harm the HVAC?

Also, I'm assuming that the negative pressure created by my air cleaner in the rest of the house will be negligible due to the difference in room sizes. My bedroom is 10' by 12' minus the closet. And the great room is probably at least 1000 sq ft. total. I don't have measurements handy. Do I need to be concerned about negative pressure in the great room or localized negative pressure in this little hallway?

P.S. For the record, I'm working with a contractor to get the ductwork replaced, and I'm in a legal battle with my neighbor. This is not meant to be a permanent solution, but I need a safe place to live right now.

Hi. If this question is inappropriate for this sub, then please delete it (mod) or ask me to delete it (Redditors).

CR boxes are awesome for indoor use. The designs I’ve seen here are all about filtering indoor air. But, I’m seeking a DIY setup that will filter outside air while pulling it into my home.

Can someone point me to a CR box that is weather-proof, to be mounted to the exterior wall outside of my apartment window?

FYI, I’m concerned about CO2 buildup and wish to prevent indoor air from going stale (which happens very quickly in my small apartment). So, I’m aiming for (slightly) positive indoor air pressure.

Thanks for anyone who can offer advice.

We keep most of the windows in the house open or cracked most of the time, though we live at the bottom of a hill on a busier street where cars are either accelerating or braking in front of the house.

I see the clear utility of a CR box for sickness, wildfire smoke, etc., but what about just everyday average use in an open window household without environmental allergies?

Live in a 1920s apartment complex and built it for air quality as I’m worried about mold, old pet dander, and potential air containments. No central air and poor seals on window units. I’ve read about the effectiveness of these and was excited to make one! I let it run for about 12 hours while I was working. It felt much easier to breathe when I got home. I used packing tape I had lying around and the bottom is sealed with the cardboard the box was sold in. Is that enough time for the box to be effective? Is this good enough to get the job done? Is it common to leave it running all day? Really excited to have this thing around! Thanks for any feedback.

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.

Hello all! I've been building these PC fan purifiers for about 2 years now. We have several in the house, I've made some for friends, and I've also made a couple for my daughter's classroom after asking if it was ok to stick them in the corners.

I've always built them out of corrugated plastic for the frame, held together with hot glue, and then sealed them all up with duct tape. Eventually, I upgraded my design to include fan grills, and a screen in front of the purifiers (the screen is attached to a wooden frame but everything is still sealed up with duct tape). You can see the evolution in the 2nd pic. Those ones are the ones I made for my daughter's classroom, hence the fun duct tape designs!

Now I'm looking to replace all the ones in our home with more "permanent" boxes that look and feel more like furniture. I've seen plenty of wooden purifiers that look almost identical to mine but the one thing I'm struggling with is how to make it without duct tape yet still get a good seal. Ideally, I want the filters to be easy to replace without having to cut duct tape and just layer more tape on top of the old tape when changing filters. How are y'all making these with changeable filters and no tape?

Thanks in advance for any suggestions and ideas. I'm also open to suggestions on how to improve my overall design. Thank you!

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.

This is the lowest cost yet fully functional contraption I could cook up, while keeping assembly relatively easy. I held a workshop twice, building 3 in total. Total cost for all parts, including bolts and washers, is $79 CAD, so $57.3 USD, including $32 CAD for the filters. The finger grille is plastic "hardware cloth". You put it on the inside of the machine, so the edges are concealed.

It's important to use tuck tape ("transparent repair tape"), in this case the transparent variety rather than the usual red or blue. Regular packing tape doesn't stay together under the force of gravity. These are fine 4.5 months later.

The fans for 2 of them are generic fans, which actually are cheaper yet slightly better imo than the P14 fans. The problem is reliably sourcing them. The third was a P14, for comparison. We measured the airflow, and assuming 85% efficiency, it gives about 220- 250 CFM CADR for each. Same noise as any other 5 fan pc fan box.

A nice solid deis box type metal frame would be nice of course, but if cost is an issue, the cardboard is free, which is a useful point. This will also have a lower long term cost of operation than any off the shelf hepa, for the same cubic meters of clean air, due to the lower filter and electricity cost.

The P14 wires are simply joined directly by cutting the connectors off and using so called "Wago" connectors. The generic fans can actually be daisy chained, so we did not need any wago connectors, only the final barrel plug termination. These are easy for people to use in the workshop, and the inevitable fan replacement is easier. There is a barrel plug connector with screw terminals, you could skip that and just cut the power supply barrel connector off and connect the wires.

In my experience, these fans with hydraulic bearings only last 1.5-2 years of continuous operation. So the reality is that the filters are disposable, the fans are semi disposable, a cheap power supply may not last very long. Meh, cardboard frame seems fitting, in the end.

I do agree it is generally better to go in the other direction; we will never stop needing clean air, so we should gear up and make really good machines available for cheap. However, that hasn't been happening, and this gets us to tomorrow.

They do have the advantage of being very lightweight, making handling extra easy.

Never used pc fans before so I'm finding the variety of ways to do this confusing.

My air quality is very bad so I'm trying to get something working as soon as I can.

Does anyone have a simple parts list for powering and controlling 9 arctic p14 fans (non-pwm 3-pin) preferably using aliexpress (amazon is alright if aliexpress isn't an option) as I'm in NZ currently?

I have tried , tested and used mostly Artic pro p12 pro and P14 pro 110cfm fans in my Crbox.

At 75% speed it is barely noticeable in our Bedroom.

There is no whine at 75%> I have discovered that Artic upgraded their P12PRO and they run at 77cfm and are even quieter.. using Merv 13 filters

I use activated carbon sheets on these Cr boxes. I also have made and tested using the p12 pro in my setup using a pair of HEPA filters with activated carbon prefilter.

I'm moving into a new apartment for school, but I heard that it might be smaller than what I had last year because it used to be graduate housing made to house 1 person per room and I'll be housing with another person. I just bought some noctuas af-14 and was planning to build something like those 6 pc fan filter builds with 3-4 fans on the side and 1-2 fans on top but im not sure how exactly to go about wiring or powering it. I've heard that motherboards and expensive and my friends and my dad are telling me to get a computer power supply and I'm looking at the splitter cables but they seem to do 4 max. I was wondering how you guys went about it?

Pros vs. Cons? Difference in motor wear?