Mario Proulx's Whole-Shop Air Cleaner [Pictures] - created 01-23-2008

Proulx, Mario - 01/23/2008.00:56:30
Hear the colors....

And I want to build it!

I have very good dust collection, but I need to get the fine dust filtered out of my air. I'm beginning to really notice it in the winter months, what with the shop all closed up tight and all, and now find myself with a bloody nose at day's end, once in a while(like, right now...).

I could spring for one of the little(or not so little) commercial noise makers, but I have a couple furnace blowers and motors that I've kept handy for just such a project. And they run so much quieter.

Does anyone here have any suggestions? Should I pick up the air close to the floor, or near the ceiling? Suggestions for filters(HEPA?)? Duct work suggestions? Other ideas?

Falco, Charlie - 01/23/2008.08:12:24
MIMForum Staff

I don't have any suggestions, but I had an air purifier in a smaller room for many years. It had a HEPA filter, and the air was very clean at all times- it smelled clean.

If you can get something with a HEPA, I would do it.

Gramann, Bob - 01/23/2008.08:35:35

Even though I have 1 micron bags, I still feel that some dust gets past them. Rosewood dust causes an asthma attack for me (After I thickness sand rosewood, my clothes go in the laundry and I take a shower). I use a HEPA furnace filter with a box fan on the floor. It seems to clean up the air within an hour or so of when I mess it up, although it takes several hours to totally get the smell of rosewood out of the air. I vacuum the filter clean when it starts getting dark--often the color of rosewood. (It's about time to get another one). Something I read suggested that this type of air cleaner needs to be near the floor, not the ceiling, because that's where the dust tends to go. In spite of everything, I still have a layer of very, very fine dust on the horizontal surfaces in my shop--of course, there's dust everywhere in the world and I don't clean very often.

Proulx, Mario - 01/23/2008.10:06:13
Hear the colors....

Thanks guys. Keep the ideas coming! Any good reading, filter sources, or websites would be appreciated, also.

I did some reading, and for my shop, I need 950 CFM in order to change the air 10 times per hour, which is my goal. I suspect the blowers to be capable, but how can be know what their exact rated flow is? They come from discarded furnaces, so the literature is long gone. Any way to mechanically measure flow? I'm sure there's a formula where the diameter, number of fins, and speed can be used to come to a rating, but where to find it? Google's letting me down....

Still haven't found anything on where the better intake is, low or high, but it just makes sense to me to have it fairly low to the floor, as dust -is- heavier than air, right? I did read one suggestion that said the intake shouldn't be between the biggest source of dust and our main work station, because that forces the dusty air to flow past us on the way to the cleaner . Makes sense. But other than that, not much...

correa, scott - 01/23/2008.10:19:26

My portable dust filter is a swamp cooler. I use paintbooth media in place of the pads. It might not be what you need but it works really well for me. Scott.

Noel, Nathan - 01/23/2008.10:20:28

All the air scrubbers I see are ceiling mounted, I guess the thought is that if the dust/dirt is heavy enough to hit the floor then that's not the stuff to worry so much about. But the one commercial unit that looks decent and I've seen running at a friend's shop is the one made by JET. It's essentially blower fan sucking in air through a filter and back out through another. The one thing that I'd change if I were to build one would be to intake through a furnace filer and back out through a cartridge filter. Choosing a blower should be pretty easy it needs to move a lot of air but not really at a high velocity and not be too loud so a Squirrel cage furnace fan would be ideal and probably the mo'quiet of the bunch.

Gramann, Bob - 01/23/2008.10:25:13

There's one page in Rick Peter's "Controlling Dust in the Workshop" discussing workshop air cleaners, and then a few pages of plans for one. He suggests (at the end of the plans) putting it on the floor. His blower is 1/15 hp and blows 450 cfm at 1500 rpm. Most furnace blowers I've seen are 1/3 to 1/2 hp. I buy my filters at Lowes.

Stewart, Dave - 01/23/2008.10:56:06
Milton, ON

The best approach I've seen (not sure it was here) was a plywood, ceiling hung box with a furnace "birdcage fan" inside & Lee Valley filter(s) (replacement filters for the unit they sell) outside. Looked fairly straight forward to build. (I'ts on my list!)

King, David - 01/23/2008.14:32:48
often headless

I'd start with an electrostatic filter from an old furnace installation. That will get you "free for life" HEPA filtration as long as you run the elements through your dishwasher at regular intervals. They use a very small amount of electricity and don't generate ozone (which you don't want.)

My downdraft sanding table serves as my room air cleaner. It runs close to 1000 cfm and has two stages of filtration. It's not quiet but anything you build from plywood is going to amplify whatever is inside. It's not hepa either but it actually does an ok job with CA fumes thanks to all the sawdust trapped in the filters. I use a 1" washable filter-foam under the table top that catches all the small parts. There's a 1" tall slot all around the sides under the top to catch dust falling over the edge. Underneath there are approximately 20' square of the pleated filter media around the sides. Ideally I'd plant it in the middle of the room to get the best circulation pattern. I don't know how important the height in the room is, I'm guessing the airborne particles are evenly distributed or they would have fallen out already.

Jackson, Brady - 01/23/2008.14:35:36

I have one of the Jet model air filters hanging from my ceiling. It runs very quietly, it has a built in timer, and really cleans the air very quickly and well. I don't have HEPA filters in it right now, just the tightest furnace filters they have at HD.

Its a very simple machine, just a box with a filter on one end and a blower on the other. The air being pushed out is way more forceful than the intake, so I orient mine so the air is blown out longways down the room, and I have a box fan in the opposite corner of the room blowing air towards the intake. Good circulation helps clean the air quicker.

I bet if you made dual filters with your two blowers and oriented them right, you would clean your air right quick.

Birko, Andy - 01/23/2008.15:56:06
Bandura Butcher

Its a very simple machine, just a box with a filter on one end and a blower on the other

They must make several models - I have one too and love the timer feature. However, mine has the furnace style filter followed by a multi-bag type of vaccume style thingy-er-other then the fan. Seems to do a good job. I hang mine from the ceiling mostly due to space considerations.

Schaeffer, Clay - 01/23/2008.17:30:27

I liked Scott's idea with the swamp cooler. It would do double duty to catch dust and humidify the air.

Robinson, David - 01/23/2008.23:31:26
future flatlander

Here is the "cave" air filter I built using 2 - 20" window box fans and couple of 20' furnace filters. The 2 fans are wired together, sealed all the edges with liquid nails. The intake filter is a standard "better" brand; the exhaust side is an expensive hepa type. Thing is very quiet and really clears the air. Cheap to make if you buy the fans off season, like now.


Lysne, Ed - 01/23/2008.23:49:54
Clarendon Hills, Il

I have a delta ceiling unit. I use it from time to time and it works ok. Big issue for me is the noise... I keep thinking of getting a furnace blower and creating something up in the attic of my shop with filters that I can change inside the shop. I find that sometimes I avoid turning on the fan now because of the noise... and I run it for short periods of time. Might be something to consider in your purchase/build and placement.

King, David - 01/24/2008.00:41:32
often headless

I guess I'm not seeing the point of these units. Ideally you'd catch all dust at the source right? If you can't catch it at the source you'd wear a face mask that catches all of it before it gets into your lungs. If you have fine dust blowing around that's not great but it will settle down after a few hours -meanwhile you still need to wear the face mask. Or you can turn one of these things on to clear the air but how do you know when the fine particulates are gone and it's safe to take the mask off? I guess I'd rather spend money getting effective source collection from the get go and take the mask off for good.

One thing I know for sure is that these units won't clear the smoke from maple or ebony on a dull saw blade. They also won't clear the smell of camphor burl or imbuya. I'd like a system the took care of the smoke and the stinky woods. Would a "smoke eater" from a bar (electrostatic filter) handle that? It doesn't seem to make any difference in the bars I've played it but I doubt those things ever get cleaned either.

Proulx, Mario - 01/24/2008.01:18:01
Hear the colors....

Yup, you're missing the point. We do collect at the source, but some always gets away. This is a method to collect the last of it. With fine enough filters and enough air exchanges, we should be able to keep a workshop at Operating Room levels... in theory .

I see using it to clean the air after my day's done as much as while I'm there. A timer will be a 'given'.

A ceiling unit has been pretty well ruled our for me, as I don't have enough headroom(low ceilings) for them, and I'd need two. Then there's the noise. But I did spend much time studying my layout tonight, and found the perfect spot for the furnace blower. It will be central, I can use my one interior wall to duct the air from the blower to the ceiling, and I have room for all these filters, including the long pleated ones I think I'll need. Seems my only remaining question is whether to have the intake low and exhaust high, or reverse it and have the intake up at the ceiling and exhaust at the floor. Either way will be the same amount of work and ducting for me to do, but it changes how I orient the filtering, so I need to get an answer to this.

I ran the nicer of the blowers tonight just to see, and it moves a lot of air. I don't think I'll need two... I may even step down the pulleys to lower the flow when all is said and done.

Oh, and I asked the library to bring in "Controlling Dust in the Workshop" as well as another similar book I've found while searching.

Debelleix, Max - 01/24/2008.03:18:26
Feeling like Galileo!

Hi everybody!

Mario, i've seen the system Lag uses in France (French guitarmaking factory) They use gravity aided dust filtration. They have grids on the floor and the air gets sucked in that way. Up to the point that the paint cabin is all gridded on the floor. I would think frool system is better. Thought i'f your workshop is cramped, airflow might be better in the air. About your furnace blowers, try to see if the compagnies still exist and ask them. But other than that, you need a pitot tube and all, which gets complicated and expensive if you're not going DIY. Myself, i think i'd make two units with the two blowers, and i'd use big torit type filters as per the cyclone i've built, with 0.5 or 0.2 microns. That means at leeast two filters per unit if you want 950cfm. (the big ones are usualy good for 650cmf) I think i'd try to make theses units with a dust box at the bottom, so you can tap them and get some of the dust out without vacuuming or blowing them with compressed air. I'm thinking of something like this Click I hope the link is OK!



King, David - 01/24/2008.12:31:57
often headless

I guess it depends. If exhaust is at the floor you will kick up any dust that settled there during the day and hopefully kick it up high enough to get it into the intake but it might just blow it around the shop until it settles in an on everything else in the room.

If intake is at the floor then you could sweep towards it and catch that dust without it billowing up into your face.

sommerville, tom - 01/24/2008.12:39:22

Hi Mario:

You can get them from other sources, but SurplusCenter (they're on the web) has a "450 CFM 24 VDC REVERSE CURVED MOTORIZED IMPELLER" that runs on 24 volts, 4 amps DC. These fans are efficient and reasonably quiet and as I recall, rated for continuous duty.

You can rig a couple of 12v DC transformers in parallel through a capacitor for the power supply. Their cheap.

If you mount the blower on the exhaust side you don't need to worry about dust in the coils. Fit a big Torrit style filter in front of the fan. There's a link in the library to a site devoted to dust collection. It has links to wholesale filter vendors.

Proulx, Mario - 01/24/2008.13:14:43
Hear the colors....

If exhaust is at the floor you will kick up any dust that settled there during the day and hopefully kick it up high enough to get it into the intake but it might just blow it around the shop until it settles in an on everything else in the room.

That's what I suspect would happen. Just hoping for reinforcement to my suspicions. I guess if it seems right, it should be. I'll build it and see...

No go in the attic. Colder than cold in winter(anywhere to -60) and hotter'n hell in summer. Even with insulated duct work, there'd be some exchange.

Methinks have enough ideas to go on and build something practical and see where that leads. Good info on filters, too; thanks! Anyone know of Canadian filter suppliers? I need roughly 1,000CFM capacity, and would like to go to a true HEPA level. I'm sure they exist...

Proulx, Mario - 01/27/2008.17:13:20
Hear the colors....

Well, I'm done! Spent most of yesterday piecing it together, and it works! I used a 4' long empty storage space between to end cabinets and under my 8' long go bar deck. I sealed up the space, then bolted the blower to the floor(with rubber feet) with the outlet gasketed to the wall(with an appropriate sized opening, or course), in between studs. two 4x10 vents at the top of the wall(one on either side) exhausts the cleaned air. The door to the area sports 20x25" filters, with the outer 2 being regular furnace filters to act as pre-filters, and the main filter being a 20x25 3M "Filtrete" filter, their finest one, also(there are various levels of Filtrete filters). Not quite HEPA territory(but very close!), but it's the best I could do locally for now, and way better than nothing!

I barely know it's running, and the vents do a great job of diffusing the exhaust s that I don't feel like I'm working in the back of a pickup on the highway...

I've been cleaning the shop all afternoon, by blowing every nook and cranny, shelf, tool, light fixture, everything. I connected a 25' garden hose to the exhaust of a shop vac, and use the air to blow every surface possible. I'm going-in every hour on the hour to blow everything, then leave the shop, letting the air cleaner do its thing. So far, it's doing great! I think a week of this and I'll have a shop as dust free as most any well kept home, as I can already see a massive improvement(and terribly dirty pre-filters ).

Thanks for the ideas, everyone. I placed the intake roughly 5-6 inches off the floor, BTW.

Proulx, Mario - 01/28/2008.09:44:45
Hear the colors....

It's a wall. With a vent at the top, and a filter at the bottom . Photo won't help much...

Proulx, Mario - 01/28/2008.11:29:48
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What the hell...

Here's the door with the filters. I have double 20x25x1" 'regular' furnace filters on the outside, and the Filtrete one on the interior. The filtrete is gasketed and fit tightly, while the exterior ones are clamped in place, but the pull of the blower ensures they seal tight anyhow.

I vacuumed the upper right corner to show how dirty it is after one afternoon's running.


Proulx, Mario - 01/28/2008.11:31:47
Hear the colors....

Here's the cavity with the door removed.... The blower is bolted to the floor, and gasketed to the wall. The wall is framed on 24" centers, and is completely hollow, so it made for a nice large duct...


Proulx, Mario - 01/28/2008.11:36:06
Hear the colors....

Here's the opposite side of the wall, showing the diffuser, and a tissue taped to the ceiling. I did this on both sides of the wall, BTW, and will add two more of these diffusers today, as they are a bit restrictive. Still, we can clearly see the air flow! I taped the tissues to see if the exhaust air was really clean or not. A handfull of these on the ceiling shows the air flow throughout the shop quite nicely and helps to show where any dead spots are, so that a small fan can be added in that area to help move the dust on cleanup days.


Proulx, Mario - 01/28/2008.11:41:20
Hear the colors....

And here's something that clearly shows my efforts are helping. These pickguards are on the bench farthest away from the air cleaner, and throughout yesterday, I would raise massive dust clouds and then leave the shop, letting the air cleaner do its thing. Some dust would settle back down, but after each session, it got better and better. After the final "blow" of the day, I swiped a finger across this pickguard, and this morning, there was NO dust on the swiped area! I suspect a week of these cleaning sessions will have collected just about all the airborne dust from the past 5-1/2 years' worth of work.


Proulx, Mario - 01/28/2008.11:46:30
Hear the colors....

And while we're at it, here's how I connect a regular garden hose to my shop vac's exhaust. This really works nicely to blow dust and dirt out of every nook ad cranny, yet the flow is soft enough that I'm not blowing stuff all over the place as i was when i tried this with the compressed air hose. Basically, this is a HVLP cleaning system


Proulx, Mario - 02/12/2008.00:00:58
Hear the colors....

well, nearing the 2 week mark, so here's an update.

The shop is noticeably cleaner! My cough has gone completely away, as has my itchy, burning nose(and nose bleeds!). Headaches are a thing of the past, also. What I'm saving in Claritin and what all pays for the power to run it, the filters, and I'm sure the materials it took. I was having headaches on a daily basis, despite a great dust collector and wearing a respirator while making dust. I also do a nasal lavage at day's end, every day, and that also proves the worth of this system(IE: my entire nasal passages and sinus cavity is much cleaner).

In other words, it kicks ass! Everyone should have a similar unit. I kid you not. I took the filters out tonight to look them over, and was amazed at what was in there. Fine, fine dust, almost flour-like. And lots of it! Yet the backside of the Filtrete filter was still white, as are the tissues taped to the ceiling at the exhausts(which I've doubled in size since the photos).

Go. Make you one! Thank me later....

Proulx, Mario - 03/21/2008.08:39:21
Hear the colors....

Update: I cut out a 12x20" opening in the wall, directly opposite to the blower, just to see if the flow through the filters would increase, and it did so in leaps and bounds, so the wall opening wasn't near enough in volume. I don't have a manometer to measure the flow, but my guess is that it's at least doubled. I'll be making up some ductwork when time permits....

I've also come to the conclusion that regular furnace filters aren't even good as pre-filters, as all the finest dust was going straight to the finest one, so I've added an intermediate pleated filter before the Filtrete filter. Still keeping one regular filter as the outermost one, since it does stop large pieces.

King, David - 03/21/2008.22:06:56
often headless

Mario, my prefilter is cut from some 1" filter foam I got in a big roll. It loads up adding several times its' weight in dust before I have to do something about it. I take it outdoors and hose it down -weather permitting, or soak it in the tub with a teaspoon of automatic dish detergent. I've been using the same piece of foam for over 10 years now. The pleated filters get a gentle vacuuming and a thorough blasting of compressed air in the driveway when the neighbors aren't looking. I find storing extra filters takes up a lot of room though cleaning them isn't exactly time wise either.

Proulx, Mario - 03/27/2008.09:07:50
Hear the colors....

Another update:

With the new, higher flow resulting from opening up the wall(exhaust) cavity, I checked to see how much restriction the filters were providing, simply removing the entire door, and found another huge flow gain. So, I'll be modifying the setup once again, changing my "door" to house 2 filter banks of 20x20", instead of the single 20x25" I currently run. I could lower the blower's capacity by changing the drive pulley to a smaller one, to better match the available flow, and still have a great system without adding to the filter surface area, but I'm going to take advantage of this blower's capacity(rather surprising little dude!).

Hope this helps!

Proulx, Mario - 03/27/2008.15:22:51
Hear the colors....

Menzel, Bob - 03/28/2008.14:16:06

Mario: when you mention in your first update that you "cut out a 12" x 20" opening in the wall directly opposite to the blower", do you mean you increased the size of the output grill? That's like putting headers on a car...much less exhaust back pressure...but I think the size of the opening could be limited to the width and depth of the stud cavity (~14.5" x 3.5" depending on how the wall was framed). Cool system, especially your use of the wall cavity for a duct. Just say NO to dust!

Debelleix, Max - 03/28/2008.15:24:25
Feeling like Galileo!

Hi everybody!

Mario, do you have any idea on the CFM your blower puts out normaly? Do you hog much wood? What's the size of your workshop? Myself i have 8X4 meters. And i do a good 120 board feet per week lately. I've caught a bronchitis and had to be in the workshop after the chairlift compagny job to finish some radiator covers, and kept on coughing, even tho i was wearing a dust mask, so i've decided to make myself a dust filter. Hence the questioins.



Proulx, Mario - 03/28/2008.16:29:02
Hear the colors....

do you mean you increased the size of the output grill?

Well, in a roundabout way, yes. What I did was cut out the wall directly across from the blower, letting it run completely unhampered(open headers ).

By doing so, I was able to guess the flow on the intake side, and if the change would have been minimal, that would have told me the wall cavity was near perfect in volume, but since I saw a huge gain, it tells me the wall cavity was much too restrictive.

I haven't done it yet(fighting chest problems right now, so making extra dust isn't wise for me at this time), but I will cut the whole sheathing off the wall out from between those studs, and build it up to give me a 10" deep cavity instead of the 3-1/2" deep one.

Max, my shop is 24'x48'. Not sure how much wood I "hog" each week, but I do a LOT of fine sanding and scraping.