I have a small (200sf max) basement bedroom wood shop in my home, and already have a decent dust collector setup. I need to add an active air filter as well. Any recommendations from the hive? The smaller Jet unit seems like a safe bet, but at $500, is it that much better than say the shop fox/wen units at 1/2 to 1/4 the price? Anyone roll their own with box fans and easier to find filter sizes?
My buddy down the street has one of these Central Machinery units from Harbor Freight. $230. Seems to work well in his small shop, but it is very loud - loud enough to need ear protection when running.
I have the Wen unit and it works pretty well. My biggest complaint is that it has a timer function that allows you to turn it on for a set period of hours at high speed but that appears to only work from the remote and because I park my car under it when my garage is a garage (most of the time) I am afraid to velcro the remote to the unit out of fear it will fall off and hit mine or my wifes car...
https://wenproducts.com/products/air-filtration-system-item-3410
https://www.amazon.com/WEN-3410-3-Speed-Remote-Controlled-Filtration/dp/B00LPD9BDI
I zip tied a 20 x 20 x 1 pleated filter to the inlet of a box fan and duct taped the edges to seal the gaps. (I have a ducted dust collection system hooked up to the usual suspects.) It gets the dust out of the air eventually and is absolutely better than not having it. I've thought of reworking a small cabinet fan I have that would likely work better but haven't done so yet.
CJ said:My buddy down the street has one of these Central Machinery units from Harbor Freight. $230. Seems to work well in his small shop, but it is very loud - loud enough to need ear protection when running.
I have a very similar unit set up for point dust collection at various tools/spots. I'm looking for something like this that filters the finer dust that accumulates in the air:
My brother and I solved this very problem. We started with a Jet filtration unit which is kind of megabucks and tried to figure out how it worked. It's really quite simple. All you are trying to do is to pull the dusty air up and through a filter. The filter medium isn't anything special, it just traps particles. And the fan part isn't magic either - it's just a matter of CFMs versus the area of the air you need to filter. So first thing you want to do is calculate the number of cubic feet in your workspace and then from there find a chart of how many CFMs you need to clean the air 15-20 times an hour.
Filters aren't magic - look for MERV ratings. Your basic furnace filter is going to be a MERV 6 or 7 so start with that in the front. It will be cheap, collect your 3-10 micron particles, and get replaced very frequently. Behind that, go for a MERV 13 filter. That's going to pickup the .3-1 micron stuff that gets by the 7 and most of your 1-10 micron particles. Finally, throw a MERV 16 in there. It will catch 95% of the 1-3 micron particles and around 95% of the .3-1 micron. You can go with a HEPA to collect more, but the dollars will increase dramatically.
Why three filters instead of one? The lower-rated filters are less expensive, so we let them eat up the Big Stuff and become more consumable. If you just use a single MERV16 or a HEPA filter, then you're going to clog them with things that a cheaper filter can take care of and fill them faster.
To pull the air through the filters, you'll need a fan. You can get some really high-moving squirrel cage fans, but we opted for a traditional blade fan based on cost. Again, it's all about the CFMs and being able to suck air through those filters.
Here's what I built:
That was the prototype that didn't have the room for the MERV6 furnace filter.
The frame was just angle iron, the filters just drop in to place, and then I skinned the whole thing in aluminum roofing flashing:
We used an air quality monitor to check their performance and they do a really good job of pulling "stuff" out of the air. Welding pollution, sawdust, paint fumes, and cigar smoke. In fact, we tested by going in and smoking a couple cigars and then closing the place up. We came back the next day and the whole shop stunk of old cigar. So we lit up more cigars, left the filters running when we left, and came back on the third day. The place had no residual cigar smell at all.
In reply to wae :
Great write-up , how long do the MERV6 furnace filters get switched out ?
there was a good test done in China by a USA engineer in his Apartment there , he only did 2 layers with a box fan but it cleaned the air as well as a $200 filter , This was for the very bad smog/ industrial polution in the large chinese cities ,
In reply to californiamilleghia :
We swapped them out once after about 8 months or so. They're probably due for another switch and to check the other filters to see how they're doing, honestly.
wae said:In reply to californiamilleghia :
We swapped them out once after about 8 months or so. They're probably due for another switch and to check the other filters to see how they're doing, honestly.
Since you already did the research what is the standard size filter you should build a box for and get the best "value for money" when buying the 3 grades of filters ?
Thanks for the info
In reply to californiamilleghia :
We just went with a 16x25 filter because it's what we could find easily on Amazon. It makes for a pretty compact design as well.
This sort of reminds me of my ghetto, box fan/ice chest air conditioner
Me and a woodworking buddy were discussing this a while ago. Our question was how long do the filters last. Looks super easy to make, four filters, abox fan and a piece of cardboard.
Hopefully the link works, not really sure how to do that
Checking back in here, thanks for input, guys. You've convinced me to roll my own. I have most of the materials already and I like that the furnace filters will be a lot easier to source and replace.
I have one of the commercial units. High end- designed for work in hospitals.
Bottom line is they really aren't much more than what is described here, except they have a $3500 price tag.
Filter change frequency is gonna vary- it will have to do with how dusty your environment is.
But I'll bet you could put an electrical load sensor or an airflow sensor which would give a signal when the flow through the unit drops significantly and the filters need to be changed.
For filter change warnings you could easily set up a manometer (gauge type or a u-bend water type) between the filter and fan. Try it with a dirty filter and a new filter. Mark the two extremes and you have it calibrated.
In reply to stafford1500 :
Yep. Or measure the electrical load variation.
Wire an idiot light to cone on when the electrical load reaches X level.
My friend has a 12 X 16 wood shop. He installed a window, put a fan in the window and puts replaceable paper filter like the ones used in home furnaces, in front of the fan.
914Driver said:My friend has a 12 X 16 wood shop. He installed a window, put a fan in the window and puts replaceable paper filter like the ones used in home furnaces, in front of the fan.
Just out of curiosity, if the fan is blowing directly out the window, what is the need for a filter?
In reply to z31maniac :
You have a point.
(All those years of setting up HEPA exhaust systems to control construction dust in medical facilities shot to hell!) 
z31maniac said:914Driver said:My friend has a 12 X 16 wood shop. He installed a window, put a fan in the window and puts replaceable paper filter like the ones used in home furnaces, in front of the fan.
Just out of curiosity, if the fan is blowing directly out the window, what is the need for a filter?
Wants to avoid a large sawdust slick outside the window? I imagine that it would build up over time...
Here's the dirtbag-cheap (grassroots) way of doing it:
DIY box fan filters – Corsi-Rosenthal box - Clean Air Crew
Note that putting a cardboard shroud on the OUTLET side of the fan increases performance.
I ended up returning the filters and fan I bought, and picking up the cheap (wen) version of a hung filter. I wasn't feeling great about the first motor that came, and was going to need to try another one anyway. It just made more sense to get the ready to go filter solution for not much more with a remote and built in timer.
Now out in the garage for some fresh air to cure paint, and help keep dust down, v1 of the window box fan w/ cheap filters worked fairly well. Clean fresh air in, and leaving the garage door cracked on the other end keeps a flow going that way. Before the next paint session, I want to throw together a frame/manifold for it to fit the window better, and position the filter collection up out of the way some, more overhead.
In reply to z31maniac :
Pulls the dust down and don't annoy the neighbors.
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