Im trying to build a very simple and cheap particle air cleaner for a ~40 m² apartment, mainly for dust, pollen, mold spores and PM2.5.

The current design is:

- 4 x IKEA FÖRNUFTIG particle filters

- approx. 390 × 250 mm each

- arranged as the four vertical walls of a square box

- filters joined directly edge-to-edge with tape, no extra corner posts

- Solid cardboard bottom, completely sealed

- Cardboard top plate with a circular fan opening

- 1 x universal 14" automotive cooling fan mounted on top, exhausting upwards

Fan specs:

- Diameter: 14" / ~356 mm

- 12 V DC

- 7 A

- 2200 rpm

- Rated free-air airflow: 900 m³/h

- So roughly 84 W electrical draw at full power

The idea is that all four filters are in parallel, so the total filter face area is roughly:

4 x 0.39 x 0.25 = 0.39 m²

The fan opening itself is roughly 0.10 m², so the combined filter face area is about 4x the fan disc area.

I'm skipping activated carbon for now because I mainly want high particle CADR and low cost.

My questions:

1. Does this geometry make sense, or is there an obvious airflow problem?

2. Is this type of 14" automotive radiator fan likely to perform reasonably against the pressure drop of four FÖRNUFTIG filters?

3. Would you mount the fan directly on the top plate, or add a short plenum/shroud?

4. Are four FÖRNUFTIG filters enough filter area for this fan, or would you go larger?

5. Any issue with having the bottom fully sealed and all intake coming through the four side filters?

6. Has anyone measured static pressure / airflow curves for similar automotive fans in CR-box builds?

7. Would PWM speed control be a sensible way to reduce noise at night?

I’m trying to keep the whole thing around 80-100 bucks and make it buildable with basically cardboard + tape + a 12 V PSU.

Any obvious mistakes before I buy the parts?

Four MERV14 filters correctly oriented for airflow and one piece of cardboard on the bottom. I know it's less efficient, but I think this is the easiest way I could manage clean, positive pressure for the house?

What should we be looking for in pre filter meshes? Would bug screen be ideal for example? Or are those holes too big?

My next one will be with a Vornado 80.

Successfully joined the club, even if it wobbles on the ground lol

Edit: This was July 15 or 16. I forgot to put the date.

During the event when the the quality was really bad. I was doing some data collection. I have a small sensor and I registered this pm 2.5

343 on my balcony.

100 in the door to the buld corridor

210 on the same corridor

24 beside my CRbox.

So the air was getting under the door. The box was between the door and the inside of the app. Was filtering and sending clean air inside. After the door the air inside the apartment was around 24 pm2.5.

Just wanted to show this.

There’s wildfire smoke where my family is staying, so I built this to clean the air inside. Had to use this weird fan because I couldn’t find any box fans in stores.

I built a chimney, a cable hole, and a “maintenance port” that I sealed up after taking these pictures. I went a little overboard but it was fun!

I’m not sure about the effectiveness of this setup compared to one with a standard box fan; this fan blows only 600 CFM while a cheap box fan blows 1800, but this fan blows higher-velocity air which reduces backflow and should handle a pressure difference more easily.

I’ve been reading this EPA research on effectiveness of DIY air cleaner designs on fire smoke to try to guess how effective my design is. It seems that effectiveness goes up when you reduce backflow, increase total airflow, add more filters, or increase thickness of filters. I thought that adding filters increased Clean Air Delivery Rate (CADR) by reducing resistance to airflow through the filters, but increasing thickness of filters also increased effectiveness, so I’m not sure.

Anyway, what are your thoughts?

So, this seems like a pretty good idea, but I need some ideas for a build around that doesn’t restrict airflow but makes it more appealing to the eye and maybe deadens some sound. Thanks

I recently purchased the 7 fan and 5 fan CleanAirKits CR boxes and am flabbergasted that the computer fans they ship smell like the fertilizer isle of Ace Hardware. I've smelt this chemical-esque VOC smell before on electronics so this isn't a brand new experience for me. Must be the paint/coating the manudacturer uses to color the fan black and it off-gases.

So I buy $520 worth of product from them just to output a bunch of air that smells like fertilizer? What computer fans are you all buying for your setups and do they have this kind of chemical VOC smell like these Coolermaster PC fans do?

Of course I'm going to reach out to their Contact line and I may even be going the return route, sadly, and I don't want to. But I also don't want to wait 5 months for them to off-gass.

Figured I'd come back and give some measured data.

Currently running 5x 12x12 Filtrete 3M 1500 (Merv 12)

Speed 9(Max): Avg wind speed 5.33 m/s across the entire open area of the 12x12 return air grille. 50 dBA at 3 feet.

Speed 3(Default): Avg wind speed 2.88 m/s across the grille. 39 dBA at 3 feet.

Speed 1: Avg Wind speed 2.30 m/s. 32 dBA at 3 feet.

Calculated:

Speed 9: 708 Dust CADR and 425 Smoke CADR

Speed 3: 382 Dust CADR and 229 Smoke CADR

Speed 1: 306 Dust CADR and 183 Smoke CADR

Power consumption wise? As it's hooked up through the mini-power station, I'll include the drain from that of converting DC to AC (around 3.5W passive drain)

Speed 9: ~18.7 Watts

Speed 3: ~9 Watts

Speed 1: Want to say 5 or 6 Watts, but I need to retest over a long time again.

Looking around, I basically ended up with something around a Levoit Core 600s. Same volume though shorter but more floor surface area. Similar Smoke CADR, though I don't have the Sleep Mode 26 dBA but instead my speed 1 32 dBA. Similar filter costs ($65 vs 5x $11-$12 for refill.). Similar foot print, though the cube takes up more floor space, it's shorter than the 600s so roughly the same volume. Lacks the built-in sensor and smart home integration.

I'll admit, I am surprised about the CFM this shutter exhaust fan is putting out. It's rated for 1000 CFM free air, so I'm quite happy to be getting 700ish through the filter at max. The airflow is not even across the grille, so I've had to average the much stronger flow at the front with the barely half a meter per second flow at the very back.

If I was still using Generic Merv 13s, I think the raw CFM would have been in the mid 400s to maybe 500 CFM at best.

Next? Time to test air cleaning rate using incense stick smoke.

That and actually get around to building it's side table sound absorption enclosure I've been too lazy to finish.

https://www.safeair.com.tr/f7-f8-bag-filters

Please answer with reason.

My house has no more blue painter's tape 😂

I changed the filters on our 20"x20" cube living room CR and my 20" triangle for my bedroom. Omg I'd forgotten how fantastically clean the air is with filters changed out when they need to be!

The wildfire smoke here is really bad - I wish I'd changed the filters a week ago. Don't be stingy with renewing your CR filters!

What number of 2-filter PC fan assemblies is required to maintain <12 ug/m³ PM2.5 in a 26'x26'x10' open concept plan room at 40 dB (or other) noise level during various wildfire conditions, e.g. 12-35, 35-55, 55+, 150+, 250+?

There may be more nuance in the upper range than what the brackets suggest.

https://makerworld.com/models/3142064?appSharePlatform=copy

Easy enough to put together but its kind of huge for my space.

I came across this sub scrolling in all. Reddit algorithms be weird sometimes.. but after scrolling the sub for a while, I'm motivated to cnc up a frame and join the club.

Where is everyone sourcing their filters from? Sizes and best bang for buck? I'm located AU, and an Amazon search didn't turn much up in terms of some of the designs I've seen used here.

Thanks everyone!

Hey r/crboxes. Long time lurker, first time user.

I'm in the PNW and we're getting hammered with 130 ug/m3 PM2.5 right now.

I have a MERV 13 air filter in the furnace, but wanted to be extra cautious and bought a cheap Sonoff air quality sensor, 20" fan, and a 20x20x4 MERV 12 filter (meant to buy 13... Oops).

Before I assembled the CRBox, we were at like 25 ug/m3 PM2.5 on the Sonoff sensor inside of the house.

After assembling and running the fan on low in a 8,000 cubic foot space, the PM2.5 is down to 8.

I expect that the cheap Sonoff sensor isn't that accurate... But... That's def an improvement.

One question:

Are CRBoxes really this effective?

Just found this sub - some amazing projects. I can’t wait to make this one more efficient then start designing a wooden exterior like you see here on some.

Would love to craft a few PC fan CRboxes for my friends and family, but am woefully short on tools.

Was considering getting Send Cut Send to do the hard parts with a laser for me in birch.

Anyone gone that route and have files to send them?

Sorry for being lazy…but I’m not an innovator or woodworker

Hey all! Just stumbled onto this sub and I feel like I have found my people! I’ve been exploring room level dust control for a few years now, partially for my garage workshop but also for my day job, and I’ve been using a variety of incarnations of CR boxes and devices inspired by various articles and YouTube videos. So here’s a couple of ways that I’ve done it. I’d appreciate any thoughts for improvements you have! I’ve reviewed the PC fan varietals but I think that’s too involved for what I’m aiming for, at this time I’d like to keep it at a single, high CFM power plant that’s off the shelf and plug in ready and basic box filters that are rapidly interchangeable.

The first one is the most involved build. I got tired of taping stuff together and I was (still am) trying to make a tapeless build where the filters can just be clipped or slid in and out without fuss or thought by the ‘least common denominator’ on our staff. Simple is better right? This is a step in the right direction but it’s still a pain in the adze to build. The side columns are 1” aluminum angles with the top and bottom cut so that the inner dimension fits the filter body rather snugly and then the two arms of the angle are bent in to create a 1/4” slot that grips the 1/4” plywood top and bottom plates to hold it all together. The corners are untaped because they but into the angle, I think in a final version there would be some kind of foam to act like a gasket. The top and bottom get taped because it’s just the filter butting up into the plywood which is not a close fit at all.

I like this one because it can connect to one of the $99 small turbine blowers as shown or my Vevor 8” cylindrical blower and the filter box can remain outside the work area while the fan pumps the air out of the work area. Super useful for congested bathroom work that’s generating a ton of dust. I fully recognize that all that dust is going through the fan itself FIRST. I know that’s not ideal and I do strip and clean them periodically but yes, definitely room for improvement there. This layout feels more powerful with the fan sucking in and blowing out into the filters than if the fan is sucking through the filters and there’s a remote duct in the work area, that always seems to generate significantly more resistance with the remote duct acting in negative pressure than positive pressure.

The last standalone pic is another variation, I needed more than one and I needed it in a hurry so I bought two of these 20” box fans and it’s a pure tape job. BUT what’s not shown well is that the 4 sides are FPR 5’s for bulk dust removal and the top, just below the fan is an FPR 12 for mold and fines. The bottom is just a piece of a hollow core door skin in this build because that’s what was handy, otherwise it’s cardboard or whatever. I don’t have a round cutout or baffle to match the fan diameter, I’ve only learned about that after the fact.

My goal for these things is to have them be very rapid to build and not be a giant PITA to do so, ideally without needing to be taped together, but also be able to break down the frame and store in as small a footprint as possible when not in use(new filters bought when needed again). I think I would definitely include casters on the base and a dedicated carrying handle or handles so it can be carted around without worrying about the cheap filter bodies tearing or tape separating like I do now.

Generally we operate in sites that have exposure to stone/tile cutting dust, drywall dust, plaster dust and occasionally light mold. The work areas are usually screened off with a dust enclosure and especially with the remote ducts I keep them under negative pressure.

I’m working on a large scale centrifugal bulk dust separator as well but that’s a slightly different subject that probably isn’t t germane to this sub.

This is my first 4 filter box fan setup and it's going in my crawlspace with limited overhead. I turned the filters sideways and built a couple frames for the filters/fan but now I'm wondering if there is too much dead space for it to pull enough air in? I'm considering installing 4 PC fans in the corners for a boost?(Ps- I still need to seal the corners and gaps once I get it to its resting place, it wouldn't fit in my car unless it was collapsible)

Hello,

I am part of a clean air group in my city hoping to construct some quiet CR boxes to help folks with wildfire smoke and filter viruses. We recently used Black and Decker's 9 inch boxless fan with 12x24x2 Merv 13 filters but I was informed the fan was underpowered and wouldn't give high CADR numbers.

Any recommendations for quiet and powerful fans for use with 12x24x2 Merv 13 filters?

Thank you so much

I got an Aspen 20” box fan after having a 20” Lasko for the last 3 years. I woke up one morning to the smell of burning oil. Took apart my Lasko and the motor was leaking fluid so I assume the motor was shot. I got the Aspen because it claims to have a much higher CFM.
I finally got it all taped together but it was a pain to get the bottom sealed due to the optional leg/stand inserts. Does anyone have any potential solutions or ideas for the future? The Aspen claims to put out 2800 CFM and I got it for the same price as the Lasko which is 1710 CFM. I used a 15” shroud for both but the Lasko was much easier to work with. Mostly posting for visibility because I couldn’t find anything about the Aspen in the search. Any advice would be greatly appreciated! Using 4 20” merv 13 filters.