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DIY premium air purifier

ryanator

Mathematical
Members
So I've been looking into air purification lately. I have an 18 year old Holmes tower room purifier that I originally bought for white noise. I never wanted to spend $500+ for the big ones (home or shop), so I came across a very simple but effective DIY method. This can be used for anything and costs around $50 total or less and moves more air than the expensive units.

All you need is:
1) 20" box fan,
2) 20x20" furnace filter
- Any of your choice, many options out there of different MERV (or MPR) ratings and filtration types commonly available.
3) Duct tape (or anything to secure it). A good secure tape will seal the air flow better. Some just let the suction itself keep the filter on (if done on the back - preferable)

The filter traditionally goes on the intake side (back) so it sucks the air in (what I do), but other's have put it on the front (though you have air blowing against the collected dust on the filter and the fan blades will collect dust to be cleaned periodically). Just make sure you have the filter air flow direction the right way (has arrow pointing which direction with the flow it should go). And depending on the fan construction (most), on the side opposite of the filter, you may have to cover the corners and sides to prevent non-filtered suction.
You will notice a good amount of suction through the filter, but air can still be sucked on the opposite side around the edges where dust will go in and blow back out. This doesn't necessarily significantly reduce the effectiveness, but can be covered to increase it's effectiveness.

This method has been around for awhile with great success, even ran 24x7 for years, no risks of fires, but motor could burn out if air flow too restricted. This can be seen all over YouTube and elsewhere on the internet. Many people have even tested using particle meters and show they significantly reduce the air particle matter as good or better than expensive HEPA filters. I've done this myself and it works great. Right now, I'm using the Filtrete with charcoal layer filter (has 1200 MPR with odor, gas, and vapor filtration) and will look at getting the straight 2200 MPR filter in the future (better air flow and smaller particle size reduction, but no charcoal layer). You can change filters the recommended 3 months depending on how dirty they get, or even get a reusable one.

Not my picture, but do a web search, and you will gets hundreds of results:
 

nodle

Cheesemonger
Administrator
That's basically all a air purifier is, your just taking the custom HEPA filter out of the application. We had a air purifier as well, but the dam filters are like $50 each. You should build a small box in between the filter and the fan and install a UV bulb as well, then that could kill the germs as well. Have you ever looked into an ionizer? I know they are bad for you and can be dangerous if not used properly, but Amazon has some neat ones.

 

ryanator

Mathematical
Members
That's basically all a air purifier is, your just taking the custom HEPA filter out of the application. We had a air purifier as well, but the dam filters are like $50 each. You should build a small box in between the filter and the fan and install a UV bulb as well, then that could kill the germs as well. Have you ever looked into an ionizer? I know they are bad for you and can be dangerous if not used properly, but Amazon has some neat ones.
I saw the UV germicidal bulbs for HVAC systems, which can be used an installed in this application too. I personally would only look into those if there is an ongoing problem that you can't fix or rid of right away (hidden mold for example). Otherwise, in an occasional or temporary situation, a good rated furnace filter (MERV 13+) will trap those same particles (fungus, bacteria, and viruses) in the filter as well (and you can exchange the filters out as often as you'd like under $20 each time). I've seen examples of people building a box that can hold several filters (in layers) that you just slide in. If I like this method well enough, I'll look into that and space enough room for an optional UV bulb.

My tower purifier has an ionizer feature on it, but I never really used it. Years later after originally buying it, I read negative things about it, and never turned it on, not really sure if I would trust using it.

Also a bonus, I cut up those furnace filters to size for use in my old tower purifier and in cabin car filter box, much cheaper.
 

nodle

Cheesemonger
Administrator
I should take the one we have and modify it to fit a normal air filter like you did. This is the one I have up in the storage shed. It's big I bet I could fit one in there.

 

nodle

Cheesemonger
Administrator
Well I wanted to say thanks @ryanator for giving me inspiration. I feel asleep after work and felt like doing something, so I went and got the air filter I posted above brought it down to the garage and went to work. I pulled the old filter out and cleaned it up. It uses a 3 way shell the back has a filter with active charcoal while the front filter is suppose to be silver lined. It's the inside HEPA filter you throw away. I got everything cleaned up but couldn't find a way to get a new filter since it's an odd size. It's 16 tall by 12 3/4" wide. But I had two brand new 16x20x1 air filters I had sitting up top that were brand new. I took my knife and cut the insides out and double layered them inside the box and put everything back together again. They are the cheap fiberglass ones that are statically charged. But with two stacked on top of each other they should at least attract dust if anything. I don't know what the MERV rating would be but I am back up and running inside with it, and it didn't even cost me a dime. Thanks for the inspiration!
 

ryanator

Mathematical
Members
I think there are great points in this thread, not only to make your own from simple materials, but can also make your own filters for devices you already have. I will point out the Winix C535, close to many "fancy" air purifiers, has only 243 CFM for air movement, and can't even get close to the CFM of a regular box fan. Without a filter, cheap box fans get over 2000 CFM on high if you want, which will lower some with a filter put on, but still retains a high CFM, much higher than even the expensive air purifier units..

I like the idea of the custom made box to make it look nice and easier to change out the filters, maybe will do that one day. But for now, duct taping around the fan secures it and seals it good, cheap and effective. Plus there are many filter options since it makes use of regular furnace filters, even high rated MERV rated ones and carbon coated as well.
 
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nodle

Cheesemonger
Administrator
Well the big box fans can move more air and therefore circulate and filter more air, but it comes with a price, the noise. Mine is pretty whisper quiet unless you crank it up to 'turbo' then it can move some air. Inside it uses a squirrel cage fan so it can be more quiet but still move some air. It also has sensors on it for night time mode where it dims the display and even runs quieter. It also has odor and dust sensors on it and can adjust it's own speed up or down based on if it sensor odor or dust in the area. I am scared to see what something like this would do in @C Pav office when it would sense odor.
 

ndboarder

Bill Gates' Gimp
Members
The Winix has 4 speeds, the first 3 are pretty quiet, the 4th is noticeably disruptive. These types are mostly the squirrel cage fans for noise, and pretty small ones, so the CFM is pretty low. They are intended for a single room though, so you'd have to put multiple throughout a house to really do much. It captures plenty of fur and dust, but I also don't really think it makes a noticeable difference in anything
 

ryanator

Mathematical
Members
Yes, most can be noisy, but that means it's moving some serious air. One possible easy solution to the noise of the box fan is doing the dual filter method of one on back and one on the front. This would cut some air flow, thus noise, but probably would be best to keep on the medium setting if doing long term so it doesn't overheat the motor. There are many people that do this successfully.

See this:
.

The guy has been doing it 24x7 since 2012 with no issues. He updates his comments regularlly, and it's useful info. The setup gives the whole room cleaner air than a $1,500 model. He jokes that his particle meter only showed the $1,500 model having cleaner air 1" inch away from it while the cheap box fan setup produces far more cleaner air throughout the room.
STILL running great, STILL no fires, burnouts or issues.STILL run them 24/7. After much testing : prefilter or not,front or back...it just works. Tested a 1500+$ "top" HEPA filter that reviewers and salesmen rave about.At the exit of the system ( 1 inch away) the air was cleaner then my fan at 1 inch.HOWEVER,at the far side of the room my fan was 75% ish cleaner air. No substitute for air flow. Conclusion : If you have some disease / medical condition that demands 100% pure air, buy a 1500+$ HEPA bigname unit and sit 1inch from the air exit and breath it. In ALL other cases.......use my setup
 

ryanator

Mathematical
Members
For the cheap sub $30 box fans, you could get the Lasko Weathershield model, suppose to be a little quieter since the motor has a heavier shield on it.

Now, if you really want to step it up, but still nothing crazy expensive, you can get a 24" drum shop fan and use a 24x24" filter (the biggest regular ones go square wise). The one below for example has two speeds, 2400 and 4000 CFM. Since it's round and fully enclosed on the sides, would be really efficient, noise on low according to videos and reviews is decent, but gets loud on high, but that would be good for some serious air filtration if case of emergencies.

This one in particular is $124, but has mixed reviews, I'm sure there are others.
 
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