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I really LOVE the way this project turned out. It's 100% practical and also looks very cool too.
When you buy a commercial HEPA (High Efficiency Particulate Absorbing) air cleaner you are basically buying a box with a fan and a replaceable filter. It doesn't matter how many extra gimmicks they add like ionisers, trace ozone generators (in disguise) or air quality monitoring units with wifi connectivity. When it comes to the crunch it's a box with a fan and a filter, and sometimes the replacement filters cost almost as much as the complete unit.
This project is for making your own air filtering unit that uses whatever filter is the cheapest to source, and either a 3D printed adaptor for a common computer fan, or some other means to attach the fan to the unit if you don't have a 3D printer.
There are two openscad scripts included at the bottom of this description. Copying and pasting the text into openscad will allow you to create a custom self-scaling adaptor for most donut style filters (or even some HEPA vacuum bags) to attach them to a standard 120mm fan.
The second script is for donut filters that are open at both sides. It prints a simple press fit cap to your chosen dimensions. This can also be used to make caps for other applications.
You can either use the fan with no guard, a standard metal or plastic one, or a custom printed one. The fan should suck air through the filter.
I chose a 12V fan and added two 1A diodes in series to nudge the voltage down slightly. This results in much quieter running and potentially longer fan life. The unit is intended to be run 24/7, so will still circulate a lot of air even with reduced flow. Power consumption will typically be just 1 or 2 watts. Running costs will be virtually zero.
Note that some fans are not suited to long spells of horizontal operation due to the design of their bearing. The whole assembly can be mounted on its side if desired. Technically speaking, the back cap could be screwed to a wall to mount the unit horizontally.
The end result is a very stylish and minimalist air cleaner that will only require the filter to be changed once or twice a year depending on air particulate levels. You can extend its life by vacuuming the exterior of the filter to remove large dust particles.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
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This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.
#ElectronicsCreators
Here's the first of the openscad scripts. Openscad is open source 3D design software that is free to download and use. This script creates the fan adaptor for your chosen filter. Measure the hole in the middle and enter it as the variable "filterhole". The other variables can usually be left at their defaults. The script as-is will work with the Silentnight filters sold on eBay in the UK.
Make sure you leave the semicolon (;) intact when you enter a new value.
//120mm fan adaptor HEPA filter
$fn=100;
//You can adjust these four variables
//Primarily the filter hole diameter
screwhole=5; //fan screw hole diameter (5)
filterhole=92; //HEPA filter hole diameter
thickness=1.5; //Thickness of plastic layer (1.5)
insert=10; //Length of insert into filter (10)
//Do not adjust anything below here
cone=(120-filterhole)/1.5;
wall=thickness*2;
difference(){
union(){
//flange
translate([0,0,0])
cube([120,120,thickness]);
//taper to filter insert
translate([60,60,0])
cylinder(h=cone,d1=120,d2=filterhole);
//filter insert
translate([60,60,cone])
cylinder(h=insert,d=filterhole);
}
//taper to filter insert
translate([60,60,0])
cylinder(h=cone,d1=116,d2=filterhole-wall);
//filter insert
translate([60,60,cone])
cylinder(h=insert,d=filterhole-wall);
//fan attachment holes
translate([7.5,7.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([7.5,112.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([112.5,7.5,-1])
cylinder(h=thickness+2,d=screwhole);
translate([112.5,112.5,-1])
cylinder(h=thickness+2,d=screwhole);
}
This is the second openscad script which will generate a cap for the other end of the filter if needed. It can also make caps for other applications too.
//HEPA filter blanking cap
$fn=100;
//You can adjust these four variables
//Mainly the filter hole diameter
filterhole=92; //diameter of filter hole
rim=10; //size of rim (10)
insert=10; //Length of insert (10)
thickness=1.5; //Thickness of plastic (1.5)
//Do not adjust anything below here
wall=(2*thickness);
cap=thickness+insert;
difference(){
union(){
//seal plate
cylinder(h=thickness,d=filterhole+(2*rim));
//filter insert
cylinder(h=cap,d=filterhole);
}
//filter insert core
translate([0,0,thickness])
cylinder(h=cap+1,d=filterhole-wall);
}

I've made some videos about diy air filters in the past, but this is a major upgrade. You see, i recently bought an actual hepa filter unit and it came with this replaceable filter in it. Hepa stands for high efficiency, particulate, absorbing filter, and it's designed to take really really small particles out of the air and to achieve a good throughput. It's got a concertina fiber in here and it's basically it's not like it's not a woven fiber.

It's just lots of criss-crossing strands uh randomly down to create a very fine filter, so it's got three levels. It's got the coarse outer to catch here and stuff, like that. It's got the pleated paper filter to give a very high surface area and then inside it's got activated carbon as a final stage and in the commercial product. This is out of you sat this into the base.

You put the base on and it locked into place and closed off this end and it simply pulled air through. That is ultimately what hepa filters are. There's nothing fancy about them. It's a fan and it's the filter.

So i've made some 3d printed components that will allow you to use a standard filter and it's scalable. So if you get a different one of these with a different hole in the middle, then by just by typing the details in the script down below in the description, you can create a custom filter. So let me show you how this goes together, because this is a donut and it's like clear right through i've got an end cap. The end cap, you choose the diameter, you choose the lip, you choose the depth, whatever you want, and it just clips in.

It is purely a friction fit i've also put little rubber feet in this, just because it makes it more stable and quieter. The other side of it is this cowl that adapts a 120 millimeter computer fan with the correct tapers to whatever size you type in so again, depending on the size, your filter, you type in the the diameter of this hole, and it will automatically create you, the Stl valve to actually fit that you also get to choose the thickness the plastic. I went for two millimeter here in the script. I've adjusted it down to 1.5 millimeter, because this took quite a long time to print the cover on the other side can be a standard computer fan.

I went to thingiverse and just downloaded a universal uh fan cover maker and customized this one slightly just to to make it look nice, but you can just use a standard. Chrome computer fan guard if you want, or none at all, if there's no risk of people sticking their fingers in, but the idea is that it's just a very simple friction fit and when you turn it on, let me just plug in oh, i should mention i Made a little adapter lead that lets you just plug a jack into this. I have put two diodes in sears. The reason for that is that this is a 12 volt power supply.

This is a 12 volt fan by dropping at roughly 0.6 volts across each diode. It just nudges the voltage down below 11 volts and it makes it run quieter. This could be advantageous and it will make the fan last a lot longer. It's very quiet for that you'll find that it takes very little difference to make a fan a lot quieter.

I hope there's not a microphone. This is blowing past. There might be a microphone. This is blowing past.

I shall tilt it to the side and i'm gon na have to check but uh. What i'm feeling here is that the air i'm getting a noticeable air force out then. But having said that, if i just even cover this, you also get a relatively high sort of turbulence of air in front. However, i know it's going through the filter because i can actually feel it blowing through between the fingers and it's not a super high rate, but that's not what this is designed for.

It's basically just a very cheap, easy to make filter i'm going to unplug this now, just in case it is making lots of wind noise. So if you look down in the description, you will find the two scripts. If you copy them into openscad, you can adjust the variables and you can make this into a custom filter. Another upgrade for the future.

Some people say and they're, probably right that these fans are not designed to be mounted horizontally because the bearings aren't designed for that. So another update might be to extend a plate down that goes underneath or just make a little stand for this, and as it is, you know it will basically just stay horizontal if you want, but by lifting up it's going to give better air circulation around it. But that will then amount to have let the fan run vertically and at that low power uh. It's a thing that you could have in your bedroom without worrying about the noise and the filter itself is going to last for a decent length of time.

But that depends how much dust you have in the air, but this is possibly one of the cheapest ways to make a fan filter and do keep in mind that even if you buy a super duper expensive medical grade filter, it's basically the bulk of the components In that are the fan and the filter and the filters are normally very expensive. If you go to buy a commercial one, make sure you check the price, the replacement filters. First, this one's affordable. This filter is about 15 pounds shipped, it's actually from a silent night.

Uh filter unit, but there we go. Let me know what you think of this experiment, make one yourself and tell me what you think, but that must be one of the most affordable and most compact hepa filter units about.

16 thoughts on “Diy cheap & quiet hepa air cleaner”
  1. Avataaar/Circle Created with python_avatars Suzuran says:

    most fans don't care what position they sit in but main issue is dirt and dust that gets inside the area over time. and orientation on that alone will determine the failure sooner or later. ive had arctic fans like those last fine in almost any state but after like 7 to 10 years of use they gotten pretty noisy and was replaced.. by that point likely getting some new ones to keep up with trend or just found something more pleasing. now best fans would be ones with the meglev bearing where it uses magnets to keep it centered no liquid no bearings work any position and dust isn't much an issue what so ever using a static pressure grade one here would make it more optimized as its designed to handle tight areas like filters and radiator/cooler fins.

  2. Avataaar/Circle Created with python_avatars Adam's Lab says:

    I made something like this for my rabbit's room to keep dust down. I used a blower motor from an old heater instead of a PC fan, it has a bit higher static pressure. The amount of hair, dust, etc it catches is insane! Definitely a good thing to have in the house.

  3. Avataaar/Circle Created with python_avatars Tristan Wegner says:

    I always enjoy your hepa videos. Can you talk about axial fans vs radial fans? Because most commercial air filters use radial fans, because they are generally able to create a higher static pressure than axial fans, which are typically only used when there is little air resistance.

  4. Avataaar/Circle Created with python_avatars Kim Forsberg says:

    Well, the fancy part of a proper filter is that structure of the filter, being able to catch particulates of the size it does, while still allowing a decent air-flow. There's plenty of sources for filters, depending on the filtration needs, such as replacement units for home air filter systems, air filters for cars etc. as well as for vacuums. I however found the cheapest, and easiest way to get a good system was to just buy a floor unit. Of course that's no fun DIY, and you are at the risk of the spare filters going obsolete as they push their next models, but it was decently cheap and works really well.

  5. Avataaar/Circle Created with python_avatars RMJ1984 says:

    I for one are looking forward to the day when 3d printers aren't just for the rich, famous and sexy people. But also for the poor, unknown and fat… Then im gonna have me some fun!.

  6. Avataaar/Circle Created with python_avatars bohdannyman says:

    This came at the perfect time. I was just trying to figure out how to incorporate a HEPA filter into my central air system. Thank you for the inspiration, the last pieces of this project just came together.

  7. Avataaar/Circle Created with python_avatars Babrahamm says:

    I modified it for a 140mm

    fan //120mm fan adaptor HEPA filter

    $fn=100;

    //You can adjust these four variables

    //Primarily the filter hole diameter

    screwhole=5; //fan screw hole diameter (5)

    filterhole=92; //HEPA filter hole diameter

    thickness=1.5; //Thickness of plastic layer (1.5)

    insert=10; //Length of insert into filter (10)

    //Do not adjust anything below here

    cone=(120-filterhole)/1.5;

    wall=thickness*2;

    difference(){

    union(){

    //flange

    translate([0,0,0])

    cube([140,140,thickness]);

    //taper to filter insert

    translate([70,70,0])

    cylinder(h=cone,d1=140,d2=filterhole);

    //filter insert

    translate([70,70,cone])

    cylinder(h=insert,d=filterhole);

    }

    //taper to filter insert

    translate([70,70,0])

    cylinder(h=cone,d1=116,d2=filterhole-wall);

    //filter insert

    translate([70,70,cone])

    cylinder(h=insert,d=filterhole-wall);

    //fan attachment holes

    translate([7.5,7.5,-1])

    cylinder(h=thickness+2,d=screwhole);

    translate([7.5,132.5,-1])

    cylinder(h=thickness+2,d=screwhole);

    translate([132.5,7.5,-1])

    cylinder(h=thickness+2,d=screwhole);

    translate([132.5,132.5,-1])

    cylinder(h=thickness+2,d=screwhole);

    }

  8. Avataaar/Circle Created with python_avatars Paul Gray says:

    The fan – it pulling or pushing as the filter layer design it seems like it should be pulled (drawing air in via the outside of the filer).

    Also the end and top caps – you leave the layers exposed so air could flow thru some of the layers and not the whole composite. So the end and top caps should cover the edges of the filter.

    Me – I'd love HEPA filters as air intake for PC case, crank them up a bit to balance out and tada, heating and air filtering PC for the winter.

  9. Avataaar/Circle Created with python_avatars kiri101 says:

    Love it! As someone doing covid-related cleaning all day I keep thinking that my activities are nearly pointless compared to proper airflow and filtration, I wish cost-effective air management was rolled out publicly and privately as far as hand sanitiser has been!

  10. Avataaar/Circle Created with python_avatars HobbyistJay says:

    There is some science and niggles around fans as well. In pc fans, if it's a sleeve bearing (probably most common and cheapest), they prefer vertical mounting. Ball bearing aren't picky, but are noisier. Fluid or rifle bearing like being horizonal, as vertical makes the fluid pool at the bottom, and eventually leak. Magnetic/maglev is still fairly new, and supposedly don't care how they are mounted. There use to be a big deal about fans being made for either static pressure, or high air flow, but now days mostly make them hybrid designs, so it's not as big a deal anymore.

  11. Avataaar/Circle Created with python_avatars Peter Morris says:

    Next step: design a cowling around the filter that tapers to a 110mm coupling. Add a tapered fan coupler on the output of the fan. Hey presto! It's an inline version that could be plumbed into ceiling vents for permanent room air filtration.

  12. Avataaar/Circle Created with python_avatars Chris W says:

    HEPA originally stood for High Efficiency Particulate Absolute. In the early 80's I maintained 300MB CDC disk drives which had removable disk packs. The drives were the size of washing machines, but even heavier. We had to replace the filters regularly to avoid head crashes.

  13. Avataaar/Circle Created with python_avatars Pp Ss says:

    A nice variation on this design would be for mounting to the back of a computer tower to eliminate dust from getting inside the case. Obviously a smaller HEPA filter would be desirable and I would print one end with the flange to easily mount it to the existing holes in the case… Obviously, one would need to ensure there is sufficient airflow after installation for proper cooling, and adjust rpm accordingly… the designs are limitless, maybe even using the rectangular ones that come with vacuum cleaners, which are usually low profile…

  14. Avataaar/Circle Created with python_avatars ro63rto says:

    I'm trying to come up with a way to repack the post motor HEPA filter for my Vax U84-M1-RE as they no longer sell the spares after only 3 years of ownership yet I can still get spares for my 20 yo Sebo X1 😤

  15. Avataaar/Circle Created with python_avatars Hunter Romanski says:

    I bought a Filtrete HEPA unit for almost $100 and the first filter lasted over a year. I replaced the $50 filter when it told me to and now 2 months later it's asking for another filter… Maybe I should just build one of these

  16. Avataaar/Circle Created with python_avatars Ossie Weinert says:

    Outstanding Clive! Very good to have during a pandemic. My 2011 Honda CR-V has a cabin filter behind the glovebox and it is surprising how dirty it gets. I have an old 12 volt computer fan and will try and make one.

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