DIY room air filter experiment 

"Always going to be available from your local supermarket..." 🤣 Oh, how quickly we forget.

Weigh the paper then leave it running for a week and then weigh it again. Would be interesting to see how much it collects

Patron philosopher of engineering - Mediocrates: "It's good enough"

Just imagining Big-HEPA knocking on your door telling you to knock this off right now.

I'd set it up with a spool to hold a whole roll of toilet paper, then have a servo to auto feed one sheet a day across the fan

Also if you want to buy fans for any filter application get "high static pressure" fans, which are quite popular with the PC watercooling community, and thus available at a reasonable price

I have one of those HEPA units,. and an important piece of the puzzle for filters is that there is a very coarse (open) filter that catches large dust bunnies. It's almost just a fine mesh, but it can be cleaned out with compressed air. It does most of the work, and it makes the HEPA last way longer. If you just put that mesh for the fan in front of the filter, it would catch most things. But given that the main filter is just kitchen roll, there's no need for 2-stage filtering, really.

The only problem you are going to find is that Toilet tissue actually sheds particles of itself, so as your device draws in air and filters out dust and dead skin out of the air, it is replacing that with paper particles instead.

I was just looking up ways to tone down the amount of dust in my bedroom and now you’ve made this video. Your timing is impeccable.

Red lights calming, that's what I'll tell my passengers in a traffic jam 😁

I made mine using an existing 7inch fan and a circular HEPA carbon activator filter taped in front, and it works brilliantly. I bought two filters on offer for £14.99 so have a spare. The air in my little office is much cleaner and I breathe easier. I have asthma, so this DIY came out very well. I used 2in wide tape to get a good air seal, switched on my fan and bingo! It works very well. There is a video showing a 12inch box fan, and all you'll need is a furnace HEP filter and a roll of 2in tape, and it's made in 5 minutes, and that works very well because my friend made one. So it's worth doing, and satisfying for saving £££ by making it ourself. I love all your videos, Clive. Don't change being the great bloke you are. I've learnt so much from your vids. You cheer me up, too!

"...And they're always gonna be available from your local supermarket." Q2, 2020: "Hold my beer!"

Random thoughts on your project: First of all I really like what you are doing! The void will serve to even the air flow across the entire area. From tests I have run on bus radiators I can tell you that the velocity across the diameter of a fan varies a lot, even reversing direction near the center. Personally I like the square grid in your current design. It supports the filter well and produces little blockage of the filter area. If you have access to a sensitive balance you can measure the efficiency of various design elements by weighing the filter before and after use to see how much mass is collected. Probably should place samples in a box warmed by a lamp to assure dryness before weighing, and run a "control" filter unit to account for variation in cleanliness of the air. I'm looking fotward to hearing your results!

There's this channel called GamersNexus dedicated to thoroughly test all sorts of computer hardware including fans and cases. One of the things they have demonstrated in several videos is how filters (or any similar materials) positioned right next to the fan decreases airflow drastically, so it's a good idea to have some space between the fan and the filter.

I wonder if having a tapered area for the filter would help? Like have a larger filter than the fan, and have ducting that adapts it. Or have a corrugated mount that lets you put more surface area of kitchen roll on the front, which would help increase airflow.

I use a disposable mask for the filter material in a small filter I have. It is not a hepa filter but it works incredibly well and has good flow.

The "buffer zone" as you call it, is called a "Plenum." :-) Nice design!!!

You could make a device that uses a roll of toilet paper and slowly pulls it across the fan opening, like a casette tape. It could run permanently for a year without touching it.

Having the void makes a lot of sense. Another thought: More cross sectional area is definitely better because of the decreased pressure drop needed to flow air through it. This is why most commercial filters have the wavy-shape instead of being flat. Similar to how a large pipe won't have as much pressure drop as a small one (assuming flow rate is constant). Or alternatively, a large pipe will allow more flow rate than a smaller one if the pressure drop is the same. You might even consider extending the height upwards into a square and putting 4 openings on the side with their own sheet of toilet paper. So you would have 5 openings instead of one: one on the top and 4 on the sides. But it would make it bigger in size and it might cause more recirculation.

You should make a plate that has magents where it meets the screws on the filter case so you can put the paper between them and turn off your computer without the paper falling.

A couple of comments. I like the idea of the void, and making it round. If you were using a smaller fan, or didn't mind an increase in overall size, you could make the top plate larger than the fan diameter and engineer a venturi effect with a shaped chamber. When testing, you could use one of your smoke machines which would generate obvious particles for showing the effectiveness of different paper types, also it should indicate how much air is directly recirculated because of the top/bottom pressure difference and how long it would take to cycle through the air in the whole room.

I use Swiffer dust pads on / over my filters to pre-filter the dust so the real filters last longer. It's amazing how much dust they capture.

Hi Clive, I worked for a computer company in the 1980's and this company felt that that office minicomputers were more useful than mainframe computers in computer rooms. Of course one of the issues was fan noise. An article was written in an internal company newsletter that pointed out that a big fan at a lower speed was much more quiet than a small fan running a a higher speed but moved a similar amount of air. Many experiments were done with geometry of the fan blades but in general the biggest issue for noise was the velocity of the fan blades measured at the tips of the blades. I propose that the you build a bigger holder that can accommodate paper towels and a slow large fan. On the bottom of the holder build in a horn (similar to a speaker horn) to direct the exiting air away from the top of the unit and also to direct it into the room so that unfiltered air in the room is mixed with filtered air and then returned to the input of the fan. You can try different paper towels for a known period of time and weigh them to determine how well the filter is cleaning the air. If someone else had similar comments, please excuse the duplication. I also suggest Wikipedia Ducted Fan and Ducted Propeller articles.

I have an air purifier from a company called Idylis. It's one of those whole room purifiers and in the instruction book for it literally says to just buy carbon and HEPA filters in large sheets and just cut it to fit inside the machine

I did this a few years ago with a bathroom fan and a round HEPA filter used for vacuum cleaner (those bucket kind of vacuum cleaners had perfect size filter for the fan). No 3D printing needed, just zip-tied them together. It's ugly but really works. Filters are cheap and available anywhere

I save used dryer sheets from when I do laundry, then I affix them to the back of my computer air intakes as filters. It collects dust pretty well and makes my room smell nice too. I change them once a week, and I can see the dusts collected and do noticed my bedroom has less dust as a result.

Red light in the bedroom is a good idea because when you shut it off, your eyes adjust to the darkness quicker than other colors.

I have a pc running in my garage 24/7. To dust proof it, I built it in a car tyre with a car air intake filter as sole air inlet. I run 3 fans as exit. 2 are mounted on the 120mm aio watercooler. Every few months, I blow that filter clean with an air compressor, and when I do maintenance on my car I replace it with the car's old filter. So far it's worked great! I had no idea that paper towels were that good though. I might utilise that knowledge when I upgrade my home office's air circulation.

Another way to measure efficiency of the filtering could be use one of those PM2.5 sensors that you can buy on eBay, to count particles in the room before and after certain amount of time with the fan running.

I like this. Place it on the floor in one corner of the room. Have it blow through some ducting and direct it to an adjacent corner of the room, near the ceiling. Have a tiny ozone generator on a periodic timer near the exhaust vent. Then have an ioniser near the ceiling, over the fan. The room is now like an efficient aquarium filter!

Interesting video, BC! Several comments to make: 1. You absolutely do want that space between the fan and the filter media. This space is called a 'plenum' in the HVAC/aerodynamics world. For one thing, a plenum keeps the filter media away from the individual 'pulses' of air pressure that are created by each fan blade as it passes a(ny) given point on the intake-side just above the blade path (and thus, avoiding a 'fluttering' effect). But mainly it increases efficiency, as when the filter media is held just above the fan blades (as your multi-hole plenum-less design would do) the fan motor hub blocks any airflow through the filter media area directly in front of the fan hub. Depending on the hub size relative to the overall fan diameter, this can be 10% or more of the filter surface area. Using a plenum lets the entire filter media surface area flow air, so it is less restrictive, filters more air per minute, and better uses the whole filter media. 2. consider using a very coarse wire mesh instead of the grid of PLA in your design, to support the filter media. The diameter, spacing, and total count of the grid supporting the media will have a major effect on the total airflow, a small effect on the noise, and will affect the filter media use (big fat grid lattice blocks any airflow through the grid supports themselves; the wire in a wire mesh is usually round in cross-section, so less restrictive than a flat plastic cross-section). It is (always?) a tradeoff in adequate filter media support vs airflow restriction/media blocking. 3. The tiny little clear rubber/silicone 'buttons' you have used for the feet on your prototype are a bit too small, and probably too stiff, to best isolate any fan vibrations. I'd use a softer silicone/rubber foot, that is thicker (taller) and softer for that. FWIW, I've been using a good ol' 20" 3-speed box fan cheapie for room air filtering. I made a simple frame of 1/2" square-section wood, with a chicken wire mesh stapled to it to support the paper towel (2-ply, only the best! lol) filter media, for room-scale air filtering. I just use a couple pieces of gorilla tape to hold the frame on the intake of the box fan. WAY cheaper than using OTC HEPA filters. I keep one running 24/7 on low speed, to tame the kitty-litter dust menace in my cats litter box area, and it works great. Pro Tip: When you go to change out the filter, first unplug the fan, and then use a spray bottle with water to lightly spray the filter media BEFORE you disturb the filter. That way, the dust/pollen/yuck stays stuck to the filter paper and doesn't just get back into the air from handling. Really helps. Tip#2: If you need to filter out a room really quickly, take the filter into another room and spray just a little Endust (or similar dusting agent) onto the filter before returning the filter to the desired room and running the fan. It makes the filter extra sticky to dust and really loads it up quicker...make sure whatever dusting agent you use, is pleasing and not full of irritating chemicals if you are sensitive to those. Love your channel, always interesting. You Scotch-re-distiller-you! :-)

This is an amazing idea, please do an update video after testing it. To see how much it can filter, how often you replace the filters

Now we know who's been hoarding all the toilet paper 🤣. Wish I'd seen this last week just spent out on a mid range hepa filter, oh well when the filter needs replacing I know what to do.

Some of the HVAC specialists on this channel would probably be best able to advise on the location and size of a plenum.

“You can always get it from your local supermarket” March 2020 - “We’ll see about that”

I would recommend to enlarge the air void further. The so called air void (duct) smooths the turbulence produced by the suction above the fan blades. And it elevates the suction power if it is made longer. I would experiment with a double that long air void. Even I propose to place a taper shaped air distribution / guide below the fan that smooths the out flow of the air to the sides. A apron like air guide at the edge of the outlet pointing some degrees downward can reduce the feed back to the intake. All these thoughts are to smooths the air flow out of the fan. Less turbulence more efficiency. That's my two cents.

Yo BC, You gotta do an EP (Electrostatic Precipitator) Filter video. High voltage...you know you want to. :D

11:11 "(toilet paper) is always gonna be available in your local super market" yeah, bout that... loved the video! I've built my own battery-powered charcoal-filter for soldering and it's the best one i've ever used! Quiet, portable, elegant, compact. If you're into soldering, i highly recommend you build one yourself. It's a fun weekend project and is good for your health. Also, once you've soldered with a fume extractor, you never wanna go back :D

The paper towel as a filter idea is genius. I've seen little 8" and 12 inch filters for hvac use, and they're about $6-$10 each, good for 90 days, thought of making a similar thing with those...but this seems to be cheaper and much more convenient. Maybe come up with a way to mount the fan horizontally, stick a few ionizer electrodes before the filter, louvres on the output side, and one of your nifty 3-d printed lamps on top. Actually, all sorts of potential. You are a real gentleman for sharing this little stroke of genius.

Hi, this is my professional/academic background. Your intuition is spot on - a "buffer" will produce a more laminar flow with a more consistent pressure differential, drawing more air through the filter more efficiently. To be honest, though, that airflow isn't nearly enough for a room, unless the room is absolutely tiny and you never open a door. Dust is created and circulated constantly - A 90%+ efficiency is great and all, but a tenth the efficiency at 10 times the airflow has the same effect on the air quality of the room. Also, you may find paper towel better than TP, which may produce a lot of paper dust/lint due to its softness.

I would've liked to see the paper after being in use for a few days.

I like this...I've been doing something similar with a 20" box fan in my shop for years. The fan sits on some wood legs and basically blows on the floor just like yours, and there is a 20x20 furnace filter on top. Not micron level, but it definitely helps in a room full of dust.

I built something similar and use it for years now. Originally intended for soldering, I ended up never turning off some of them. In case I open my window on new years, those filters clean the room in less than a minute when I have them on full blast. One version uses a fin grid array on the output and that helps to direct the air in the direction it blows into. A unaided fan will blow most to the sides, as that is where the centrifugal force throws the air. Your idea to space the fan and the filter is pretty good. When the filter sits close, most of the air will just go in through the centre of the filter and the sides will stay clean. With a spacer like yours, the filter is used more evenly and will last longer. Maybe you can build a tower like spacer that allows for filters on the side, so the bigger filter area makes it easier for the fan to pull air through.

Interesting. My girlfriend is allergic to pollen and recently we invested in an air purifier. It's really just a big fan with 4 different filters for dust, pollen and other particles as well as some kind of sensor for air pollution levels. The filters are very expensive, so hearing that paper towel is an effective air filter is very interesting indeed.

For the next iteration, I'd consider automatic replacement of the filter. Imagine ancient scrolls. But motorized. So you'd install a new roll of toilet paper once a month.

You should build an automated roller so that you can stick an entire roll of toilet paper on it and have it cycle one sheet per day/week/month. That way you don't have to deal with it until the roll is empty.

Excellent idea. Thank you for the inspiration. I like the dirt-cheap filter-medium concept of using tissue rolls. Couple of suggestions: Add a good length of clothes dryer exhaust hose to the exhaust side of this filter. That will prevent ineffectiveness problem of exhaust air looping back into the input. Use an exhaust plenum with hose attachment cylinder on the side and the fan mount on the top. The air intake / filter-medium-holder could consist of a cube shape. You'll have 5 sides for filter-medium and the bottom side for the fan. Drawback is that you will be needing something to hold the sheets in place, because your fan will only start to hold them in place when all 5 are in place. This shape would eliminate the need for an intake plenum. I'll start with a test rig, which will later be converted to a portable solder fume filter on Li-ion. If you're interested in experimenting with different kinds of fans and their static pressures and you don't have any pressure measuring equipment, may I suggest a good length of transparent aquarium bubbler tube. Fix the end of it in a vertically oriented U-shape. Put some water in that U-shape. Liquid levels in the legs of the U are equal, unless you apply slight pressure or vacuum to the other end of that tube. Set a ruler next to it, so you can put a number on the fan's performance. You can print your plenums with test ports where you can attach this pressure test tube, or just drill a hole in an existing plenum. Don't forget to plug the holes when not measuring.

Nice idea! It's small enough to sit on a night stand, creates a little light, a little white noise and filters too. The toilet paper or paper towel concept works from ease of use and maintenance. At work we buy filter media in rolls but that's not something your average household would be able to buy easily.

Even if it fails as an airfilter, it's at least a perfect way to dry your toilet tissue!

You should buy the "extra soft" loosely rolled toilet paper so you can have the privilege of paying twice the price for half as much.

"They're always going to be available from your local supermarket..." -Famous Last Words. ;-)

Back in the early days of home PC water cooling a company sold an acrylic air void for the radiator (car heater core) that actually made a big improvement in cooling because we didn’t have fans designed to deal with the airflow restrictions of a radiator. I think this is a really good idea and would love to see a single or even dual 12cm fan housing, as there are many 12cm fans available that handle static pressure much better without making a ton of noise

The thing with HEPA filters is that they positively bind the particles inside so when you are changing it you are not releasing the particles back into the room 😁

Add a bog roll holder, and a small motor to gradually draw draw the paper across and roll it up on the other side. Maybe use the some clock mechanism, e.g. Flipclock.

Ok Clive, you finally tickled my synapses to the point I just had to jump up and respond. In a past life I was a flowbench pilot, and have had my digits in many a port and orifii (word?) trying to get the best out of whatever was thrown at me. Just remember....you asked ;) I would use the bigger fan, but only after chasing around the edges of the fan blades with a sharp x-acto blade to trim off any and all molding flash and imperfections. Radius any blunt or sharp edges. Even do the same to the inside of the housing, anywhere air will travel past a corner or edge. Also your idea for a plenum (air void, in Clivanese) is a good one, as the blades would create pulses passing so close to the twalet paper, resulting in possible additional noise (turbulence). Less turbulence = less noise. A plenum is basically a reservoir, of air in this case, and air does 'stretch', so any pulses or noise may be lessened being further away from the aforementioned square of butt tape above it. Also, a round housing to match the diameter of the fan blades would help with aerodynamics, as the air wouldn't have anything to 'crash' into...yep, turbulence and noise again. Also would possibly increase the flow volume slightly, not having to fight with the air that just crashed into the square corners on a round inlet. Having a tapered, or funnel-shape, to the round plenum would smooth things out even more, with the entrance being larger than the bottom. Possibly with a round fan grate found on many computer cases. Round wire will flow a bit more smoothly than a squared-off grid as you have currently. Also it would allow a larger piece of bunghole buffer to be set on top, increasing the swept area of the filter, while also being less restrictive...and allowing even more air in. I could keep going, but I've already started to put myself to sleep. Best of luck on this development project, and remember to keep your thumb away from the filter...nobody likes a hole in their TP. Salutations from the southeastern Michigan swamplands.

I decided to look for an alternative to those expensive room hepa filter devices several years ago. Ultimately I ended up just getting a few $20 box fans and taping 20inX20in hvac hepa filters to the back. Obviously these aren't very quiet even on low but they move VASTLY more air through the filter medium than even the beefiest "room" filter and for considerably less cost.

I would think the air void would help if only because it'd do a better job of distributing the air pressure across the whole filter. It probably doesn't need to be very deep though.

Air void yes, but for the holes, I would imagine that the more open that it is the better. So, the filter support needs to block as minimal amount of air as possible, while still supporting the filter.

Like many people and yourself have figured out, an air void is a good thing. It is actually called an air plenum chamber. It equalises pressure, reduce sharp corners for the air stream and reduces noise. Bigger is better generally. As someone else has already stated he uses the disposable masks for the filter element. It is made with Polypropylene PP spunbound and melt-blown nonwoven fabric. You can also buy activated charcoal inserts for some types of masks. If you choose to use the disposable masks filter media, try to 3D print a mound on the intake side. This will spread out the folded pleats in the mask. More area equals less pressure drop and higher efficiency rate.

You need a much larger filter to reduce the resistance. That is usually done by pleating the filter media. A higher powered fan is also needed unless the room is very small and is sealed off from the rest of the house.

There is some good DIY air filter advice at a site called air-purifier-power. DIY ideas on foam prefilters, reusable activated carbon, bulk filter medium...

While the multiple circular holes are aesthetic I think the first version with the cross bars would be better. The air flow of the "holy" one would be restricted as less open surface area.

Chamber between fan and filter: good idea. You are correct about it regulating the geometry of the air flow and using more of the paper. This in turn reduces the air resistance and increases the flow rate. It might be interesting to experiment with baffles to straighten out the air flow and reduce vorticity in the chamber, and possibly even ducting to direct the air out the sides after the fan.

I have a standard Blue Air Pure 411, and although its fan frustrates me a little with its on, loud, and very loud settings (we have it on the lowest as a small amount of background office noise), compared to the DIY efforts, its cylindrical pleated filter design means that it's probably got 100x the surface area of your bit of toilet paper. It's only rated for a small room too - unless you live in an extremely well sealed house, your standard room air movements are going to be significantly greater than what your little filter could deal with. If I was to DIY another (and I've been considering it), I'd be making my own cylinder and fan unit on the top, and buying the same replacement filters to put around it. Also, a pre-filter is basically essential to prolong the life of the main filter - ours gets visibly dusty and has a brush down every month or so, and you can simply throw it through the wash every so often too if necessary.

Nice project. I use kitchen towel as "filter" in my robot vacuum cleaner. Works better than the original fiber version - and as you point out, easy to replace. I think the bigger/larger distance between inlet and outlet the better circulation of new (dirty) air. Less air short circuit.

If you were to fold pleats into the sheet it would increase air flow and filter efficiency by turning it into a depth filter.

Clive thats brilliant, I never thought paper towel would be any good for filtering. I think the Air Void is a good idea, if nothing else, it will reduce the recirculation a little. I'm thinking this would be perfect for capturing dust therefore reducing the frequency of the need to dust the furniture too. Looking forward to more on this ingenious project.

I built one years ago with a fan either side of a spherical "expansion chamber" that had some foam in it. the amount of dust that thing pulled out was unreal. using a black orchid hydroponics fan that's inserted into and old car airbox/filter now and that works really well. Even better if you can exhaust to the outside and use a lighter filter medium.

I remember eons ago an ashtray that had a fan and filter built in. It worked best if you didn't actually use the ashtray. And didn't smoke.

Unfortunately, there's a reason that any air purifier (that has any non-negligible effect on the amount of particulates in the air) is large and (at least slightly) noisy. Unless you live in a sealed bunker with precisely zero drafts, I strongly suggest you run some numbers on the air flow rate that you'll need in order to compete against the rate of introduction of new particles from the outside (not to mention the generation of new particles inside), as well as the pressure drop across the filter *at that flow rate*. Also, given the high pressure drop typical of decent filters, I believe it's fairly important to use a fan specifically designed to provide a high static pressure, or else you'll end up on a really bad place on a normal fan's flow rate/pressure drop curve (which, specifically, would leave you with a very low actual flow rate for a given amount of noise/power). Basically, unless toilet paper is somehow a magical filter that is orders of magnitude better than other specifically engineered filters that have come before, this absolutely doesn't pass the sniff test -- please beware of tempting people with health problems away from the actual air purifiers they need to save a few $$$ to end up with something that absolutely doesn't help with their allergies or asthma. I saw this happening first hand during the Sydney Bushfires with similar homebrew "air purifiers"; very sad to see not-so-well off people wasting their money on actual junk.

bonus thought: when you are talking about the pattern of holes at 10:00 - you can model a solid block and give it infill, walls, but no top or bottom layers in the slicer. this leaves the infill pattern exposed on the top and bottom. it can look amazing and would allow air to pass depending on the infill pattern used.

Perfect coincidence. My budgies peaked their heads into our AC vents and chewed/destroyed the internal PP filter mesh. I was going to buy a new filter but now I'm thinking of sticking some layers of paper towels. Thank you.

Use two plates forcing convolutions into the filter paper to increase surface area!

What you designed is perfect for a bench solder sucker.. pulls away from face and the circulation would be perfect. Try that and see what flux etc is gathered. I concur with Mark Garth.. use your HVAC friends and have a plenum review. (Just had a flash of five bearded wonders with overhead spot light on tiny fan all smoking cigars and pondering). Also you can by bulk HEPA and MERV filtration media, but can also take apart a low MERV comercial filter.. sometimes cheaper.. like a 3M filtrete and 'take it to bits' . I like the idea of just having it suck the media - at least for bench and like an electronics room filters. easy to change when you think of it.. have a slot on side for media. haha could also print one for bathroom and have TP roll pull over fan :/ ? dual use - first filter then err no waste anyways)

FEMA and other folks worked out the best improvised HEPA-grade air filter was pushing rolls of toilet paper through a solid baffle with holes cut into it. This was for fallout shelter purposes, so filtration of very fine particles was a criteria. You make many holes in a big baffle and put many rolls through the holes (they should fit tightly) in order to bring down the (parallel) resistance to flow. Still and all, a positive displacement pump or something with a lot of vacuum is required.

Hi Clive. You do need a chamber in front of the fan to assure good performance. Don't exactly know the theory behind it but it is definitely needed. We manufacture electronic control equipment for micro hydro systems and on our panels above 60kW the heating require fans with a spacer between heatsink and fan. We make our own from steel and they are 20mm deep. Commercial ones are about 30mm but our experiments showed 20mm is just as good. Love your channel. Keep up the splendid work. Best regards John W.

It's also possible to make cylinder with mesh on the side and closed top, then roll toilet paper on the side, this will make much bigger surface for a filter

I was startled that there were week old comments on a 13 minute old video, but then I remembered Patreon existed

Hi, Clive.. I have recently built a wood lathe with the same style of air filtering for the motor and the electronics cooling. (PC fan + furnice filter fabric) The only difference in my version is, that i have made a much bigger "Filterbox"....to give me more filtersurface. The void in front of the fanblades helps to straighten the airflow. (...kind of flow straightener..) I like the toilet paper approach. Its so simple and ingenious...

The buffer/plenum is important. The longer the better, 1/2 to 2 times the cross section. The filter area needs to be increased 50 fold. And still I think the system capacity is going to be disappointing. But, it's the fun of the build. Thank you for sharing what you do.

Awesome idea Clive. I know its off topic and all, but can you please do more of your old Trash Cooking? Me and the wife both love those videos!

Hi Clive, Very smart idea IMHO I think it makes sense to have a cavity as you designed. I think the cavity will negate or absorb any turbulence at the surface of the spinning fan .

I like your idea. Still some suggestions: 1. increase the paper area, like use a zigzag frame or a angled setup with a long side (the airflow can likely still pull the filter into place) 2. Use a radial fan instead of a axial fan for more pressure (may not be needed if 1. is taken to extremes) 3. Scope creapage: use a motor to slowly pull the paper across the fan inlet and onto a "used" roll, to keep the filter medium fresh/clean. Note: may need a super-slowness controller. 4. Scope creapage: Use scented paper for freshness

A lot of wood working shop owners also posted really good videos using forced air furnaces filters. Many use that in combination with a cyclone to remove the finer dust with the furnace filters. The cyclone typically only remove the shavings because the bags arent that great.

I've seen carpentry workshops that use kitchen rolls for filters on the giant sawdust extractor vacuums. Far cheaper and just as effective.

ive done this i recommend A very strong fan 12v 0.45a-5a and waiting around a month with it on full blast 24/7 you will see a slight decolorization so it does somewhat work

I'd like to see what the current draw is using different filter media. The void is definitely a good move, and will also allow eddies to move freely over the fan blades without having a stalling effect on them. Good vid and food for thought.

For those in the cheap seats out there, it's pretty easy to make something similar to this. Just take a cheap fan (120mm or whatever size you're working with) and rip the blades, motor and wires off. The frame can be used as a spacer and a grille for mounting your filter. Then all you need to do is figure out a 12V DC power source, which is pretty easy. It's always preferable to use a pressure-optimized fan like a Noctua P12 Redux so that you get a solid volume of airflow through the filter. Gluing neodymium magnets onto the frame could also allow a magnetic dust filter to be used for quick replacement and holding the paper filter in place.

Found myself a new project 🤷 Having outdoor/indoor pets means dirt and dust on everything, and this seems like a good idea to me 👌

You can buy sheets of carbon or hepa filters cheaply for eBay and cut to size. That's what I use for my soldering fume extractor

I think the air void is a good buffer for the paper. I do think it could be half of the thickness you currently have it at, and it would also save on 3D-printing costs. And you can probably use a long plastic pipe in which you cut square holes, to get the air from one corner of a wall to the other corner, to effectively filter the air. The walls of the buffer zone also increase the length of the duct of the ducted fan, which increase it's efficiency even more, by not reusing the same air. But you can also have a large pipe with a few holes drilled, the further the bigger the hole or the more holes of the same diameter, so you can use a single small fan to clean the whole room. Or so you can have such a cleaning pipe on opposite sides of the room, most efficiently having the fans being on opposite corners of the room, to create a very slow cyclonic effect, which would help push the dust towards the walls, where the fans would filter the air. The filter can still be behind the fan, but you probably need to make an adaptop from the square fan to the round pipes.

The plenum is a must do for optimum efficiency. As a rule of thumb, it should be 3 times the diameter of the fan away. I worked in industrial maintenance for many years and dealt with many contractors who installed air systems. Most all used that simple rule. It also applies downstream, before the duct takes a turn or size change.

I'd like to know if it does anything. The idea is great, but I'm not sure that small of an area will ever filter the air in a room... Will watch for updates!

I would like to see the change in current draw with the different materials

Neat idea, with two notes/concerns I can think of: Filter performance is not just about how much particulate they block, but how much particulate *for a given resistance to airflow*. While the toilet paper or paper towel sheets might do a good job stopping particles, they're also impeding flow a lot more than a purpose-built filter medium would. Secondly (and compounding the first problem), axial computer fans like that are especially terrible at pushing or pulling air through obstructions, doubly so when they're slow quiet ones like this; they're considered very low static pressure fans. Combined with a high-resistance filter medium, this means you will not move very much air through one of these for its size and the (low) power it consumes. You could mitigate this by changing the filter medium, substantially increasing the surface area of the filter by increasing the diameter of the filter area relative to the fan or adding corrugations, or you could switch to a blower or squirrel cage style fan which tends to operate better with obstructions (this is why you often see this style of fan used in HVAC systems I suspect).

I did an experiment last summer where I took a huge empty coffee can, took a small baby pillows case made of 100 cotton, made something like yours. The case was the coffee can and a 12v fan running at 5V, and rubber legs made it nice and quiet. The plan was to empty the bag in a preheated BBQ every so often to rejuvenate the charcoal, and when it stops smoking, the charcoal would've burned off all the contaminants and good as new. However after 6 month, the quitting force got the best of me and I just couldn't make myself do it. The force is strong with me. So, I bought a commercial air cleaner from Amazon. It's hepa filter based, and has a thin and flimsy carbon filter in front of the heap part. I rather fork out $12 every 6 months for replacement filters, than to sing and dance the DIY way. The filter has UV light (probably fake) that I've never turned on. Your way is cheapest and very practical. I can't wait to see your improvements. An Arduino that drives a stepper motor and unwinds the toilet paper one tissue every day? Like a cassette play for ass-wipes?

I think that your circular holes look great and I understand you've done them for aesthetic reasons although I do wonder about the total surface area being reduced?

The void between the fan and filter will even out the lower pressure below filter over the whole surface. Also having the fan blades too close to the paper will cause cavitation, which will reduce fan efficiency, and create noise.

Great simple and workable design. What you could, add is a magazine for a toilet roll, incorporated with the fan box. Rather like an old 35mm camera. Just wind onto the next sheet when used, eventually remove the whole used roll and empty straight into a bin. No need to touch the used paper.

An interesting idea. I look forward to seeing how it evolves. You ideally need several prototypes running simultaneously to compare the degree of dirt build-up on the filters. I wonder if a high voltage static charge on the filter would increase its effectiveness. Maybe you could incorporate a negative ion generator too, or add a small trace of ozone.