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u/last0nethere_ Jun 07 '23
Why put a shroud on? Genuinely curious, not questioning the design or LPT
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Jun 07 '23
[deleted]
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u/kipkoponomous Jun 08 '23
Please use your last three sentences or some version of them to explain this concept in the future. Excellent explanation.
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u/dave1carney Jun 07 '23
if you take a piece of paper towel, and hold it against the fan, you can see the parts where it blows (towards the middle), and where it sucks (towards the edges). If you tape it shut, all the suction has to come from the back (where the filter is).
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u/marino1310 Jun 08 '23
It minimizes air leakage. Like water, air will take the path of least resistance, if there is too much backpressure air can leak past the edge of the blades and be pulled in from infront of the fan. The shroud makes it more difficult and increases static pressure
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u/heysoundude Jun 25 '23
The shroud is like the winglets on modem jetliners, which are there to basically make the plane more stable and efficient. There is a pressure differential created by the fan blades similar to wings (or the air wouldn’t move), but at the tips of the wing, the high pressure sneaks around and reduces the low pressure (so it doesn’t push as much air). This videomight help, if you consider the high pressure under a wing keeps the plane up in the air, except in our case it moves the air through the fan (and the filters before it). If you really want to dig deep into it, look at ducted propellers/fan blades. It’s the basic concept behind toroidal fans and props showing up in my YouTube feed these past few months. (There, have a rabbit hole to fall down)
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u/WideStrawConspiracy Jun 07 '23
Why not just put one filter directly onto the fan?
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u/spacekronik Jun 07 '23
Causes it to lose too much air flow is my understanding. I use one of these as a saw dust collector at work and it works amazing
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u/WideStrawConspiracy Jun 07 '23
That makes sense... My AC tech told me to start using super cheap filters because our old blower can't keep up anymore.
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u/AsphaltAdvertExec Jun 07 '23
My old AC tech from work told me to use the filter that has the best airflow if you want to extend the life of your system.
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u/greengoldblue Jun 08 '23
I use a 2 inch thick filter with lots of pleats at the intake vent. More surface area equals less resistance
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u/jbourne0129 Jun 08 '23
I tape a 2" filter directly to the back of a box fan and it's no problem. It moves plenty of air, been using the fan this way for years allergies
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u/SpareiChan Jun 07 '23
Correct, I got some 20x20x5" Merv 13 filters (got lucky and got NIB from a surplus contractor store for 90% cheaper) that I can put up to it, thicker cassettes usually allow a greater CFM (airflow) and less resistance than standard 1" thick filters. If you go to high on the merv raitings it can actually damage the fan motors (this also is true for home HVAC) but for a cheap 30$ box fan IDC that much.
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u/dnuohxof-1 Jun 07 '23
Topically relevant to anyone in the NE US right now choking under the wildfire smoke from Canada.
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u/abductee92 Jun 07 '23
This is how I built an air cleaner for my workshop. Works great for sawdust.
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u/pandaSmore Jun 08 '23
So just to be clear. You're pulling air into the box, correct?
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u/Mono_831 Jun 07 '23
Can I cut a hole in the bottom to put my head through and just walk around with a suped up helmet mask?
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u/-Cyy Jun 08 '23
I made one of these a few months ago, pretty easy. Took maybe 10 minutes to put it together for the first time.
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Jun 08 '23
[deleted]
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u/-Cyy Jun 08 '23
You just replace the filters after some time, save as an air conditioner. I read somewhere 6 months to a year dependimg on how often you run it and the environment it's in.
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u/satori0320 Jun 07 '23
Great idea, though the version I've seen is turned 90° with the fan blowing straight up.
For doing taping and bedding, and the sanding afterwards... This thing would be awesome.
Same with demo of old bathrooms and showers... Trap all the bullshit coming out of the mouldering walls.
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u/Georgep0rwell Jun 08 '23
As seen on This Old House?
https://www.thisoldhouse.com/green-home/22231148/diy-air-filter
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Jun 08 '23
[removed] — view removed comment
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u/h0rsepow3r Jun 08 '23
You can do that, I've built them that way. But you'll get way more air flow by using four or five filters.
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u/WaitForItTheMongols Jun 08 '23
Good filters aren't cheap and these things are super janky. I priced it out and determined that a commercial Coway air purifier, with PM2.5 sensing and active power level adjustment, doesn't cost much more and doesn't look like a cobbled together mess.
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u/jbwilso1 Jun 09 '23
Actually made one of these recently! It works far better than I ever expected I would. My mom and I invested in a $2,000 couch from Ikea recently and we have four cats that chill on it constantly.
We had invested in things ranging from cat spikes (exactly what it sounds like. Basically a blanket of spikes that supposedly deters cats and totally fails at it (however, my orange tabby George gives this product five stars) all the way to these shiny silver things that are similar looking to emergency blankets tht make a lot of noise that cats also supposedly don't like. They seem to enjoy making noise with it all day.
Anyway, all of these things specifically targeted at cats seem to fail at keeping them off of the couch. So after resigning ourselves to the fact that we just spent $2,000 on essentially something for them to puke on and have to remove cat fur from, I it's awesome dude on Tick Tok had made one of to keep down the dander & fur from his multiple dogs. I figured why not... It was probably one of the least expensive potential Solutions we had tried.
I have to say it's one of the most effective for sure. It kind of looks like shit, but it is effective. If I can remember, I'm take a short video and post it here.
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u/joshhazel1 Jun 09 '23
I knew for sure this was legit and quality product when I read the final step of duct tape. That will hold anything together.
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u/DauOfFlyingTiger Jun 08 '23
This is literally a life saving hack. Great for Covid and wild fire smoke.
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u/cherrycoke_yummy Jun 07 '23
ooooor you can just turn on your furnace fan!
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u/heysoundude Jun 19 '23
I would wager that one of these cycles/cleans the air significantly more efficiently
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u/HeartlesSoldier Jun 08 '23
For the cost of all those filters, the fan, in the time and labor... I'd rather just find an old air purifier on OfferUp or Facebook marketplace. Too many people buy a new one for superficial reasons such as needing a new filter, needing to clean the old filter, or wanting a different model.
Just spend 20 to 30 bucks instead on a used one and fix it up like new, that way you get all the bells and whistles featured on a name brand unit, as well as not have something that looks like a science fair project in your corner
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Jun 09 '23
This CFM this design produces is about a 200 dollar retail design equivalent that is approx 50 usd to make. Its popular for a reason.
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u/HeartlesSoldier Jun 09 '23
And I got a $300 retail unit, for 45 bucks. It looks nice and works well. It just needed a little cleaning which is probably less work than it would take to put this together.
I guess it's different strokes for different folks but in the end we can all save just as much money
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u/Opinionsare Jun 08 '23
I am think that I can apply this to flow through ventilation of my house.
Getting filters close to window opening and sealing them, then using a small window fan to draw fresh air through the filter.
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u/h0rsepow3r Jun 08 '23
If you can use a 20-in box fan, just tape a filter to the back of it. I do that in the windows and my sliding glass door.
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u/SciFidelity Jun 08 '23
Where would be the best place to place a filter like this?
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u/h0rsepow3r Jun 08 '23
Centrally located in the room or house. That's not really feasible for me so I have them a few inches off of a wall. You may need more than one depending on the size of your space. One of these with four filters running on high is way overkill for a bedroom. You'd be better off just taping a single filter to the back of a box van and making a front fan shroud for a bedroom.
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u/SciFidelity Jun 08 '23
This will be in a basement that's now a living room/bedroom pretty big open space. Just not sure if it makes sense to have it closer to the back of the room or closer to the stairs/exit may just play around with it and see what works best.
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u/h0rsepow3r Jun 08 '23
If you have the room and don't mind the look, the center of the space is best. If the space is around 600 ft², I'd say it's going to clean the air pretty good no matter where you put it, if you run it on high. I do that when I'm not around, and then turn it down when I'm home. It's working pretty well I must say.
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u/mvk2424 Jun 08 '23
Is the fan blowing into the box or away from the box?
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u/heysoundude Jun 15 '23
I would think that you’d want the filtration before the fan, so it’s on the “suck” side of the fan, or the fan is blowing away from the box.
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u/pisandwich Jun 08 '23 edited Jun 08 '23
Just a 20" box fan with a single 20x20x1 high-grade home HVAC filter is plenty of filtration. Way more surface area than the filters on those consumer grade hepa air filters too. Just make sure the airflow indicators line up and seal the filter to the fan casing really well.
The 3m filtrete 1500 is good for smoke and mold spores and some viral/bacterial filtering. Still has good airflow too.
Doing a cube structure like this would be very bulky.
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u/wan314 Jun 09 '23
I think it is to increase the airflow so it doesn’t strain the fan
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u/pisandwich Jun 09 '23
It does reduce strain on the fan technically, but it's unnecessary. I've been running a single filter on a 20" box fan for 4 years without issue. You can get the 2" deep ones to reduce restriction also.
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u/heysoundude Jun 15 '23
I’m waiting to see a box fan filter setup like this that uses a brushless motor with PWM controller and toroidal blades. YouTube is a great resource if any of those are unfamiliar.
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u/Fairly_Suspect Jun 07 '23
This works fine but if you are on a budget just tape one to the intake side of the fan.