A number of people have been asking me about the air scrubbers that I build for my shop, and how would they go about building their own. I’m making this available to everyone, as I believe that every wood shop should have one (or more), and anything that can make for a safer and healthier work environment is a good thing!
Any scrubber that you build can be easily modified to accommodate either a timer mechanism, a remote switch, or both. (Cheaply too!)
There are two ways to build an air scrubber – the expensive way, purchasing all new components (e.g. blower) and materials, and the inexpensive way scrounging and recycling components, and using any scrap plywood that you may have. I am always a fan of the second method, for obvious reasons, but also because I like the challenge and satisfaction of revitalizing something that may have been destined for the scrap heap, and reinventing it into something completely brand new.
The first step is to determine your shop’s total cubic feet of air space. Use the formula (Length X Width X Height), divide this number by the number of minutes it takes to exchange one full air volume. The rule of thumb is that a scrubber should be able to exchange the total volume of air a minimum of 6 times each hour. The more exchanges that can occur the better.
Gathering the materials: The heart of the air scrubber is the blower unit. (Without it, all you have is a nice looking box with some filters stuck in one end!) The blower’s CFM (cubic feet per minute) capacity should match the number that was determined from the above formula. The best scrubber blower is a continuous duty “squirrel cage” unit. (The Grainger catalog lists these as Shaded Pole blowers and Furnace Blowers.) This is where scrounging and recycling start to pay off. The blowers that I currently have operating in my shop were salvaged from large home furnaces, and from whole-house humidification units. These units are capable of 1000 CFM’s and 600 CFM’s respectfully. They cost $0.00. (Yes, if you can believe it, at some point in the last 30 years, builders here in the North East thought that sending heavily humidified air throughout the entire house from a large water/blower/duct unit in the basement was a good thing!) Talk to your local furnace installer regarding a used blower unit. When new furnaces are installed the old units are just scrapped, usually with the blowers still fully functional for your needs.
The body of the scrubber can be made from a (approx.) 4’x4′ (x 1/2″) plywood, some 1″x2″ pine, a random assortment of nuts, bolts, washers, and screws. Additionally, you will want some foam gasket, a switch of your choosing, and you’ll most likely need to fabricate a power cord (16/3 SJ) and plug.(grounded triple prong).
Before you start building you’ll need filters. (The box unit’s dimensions are partly determined by the size filters that you choose.) There are pocket filters and there are pleated filters – I use the pleated filters due to their low profile and the fact that many of today’s filters can match the performance of good pocket filters. Either filter will work, it’s your choice. To extend the life of either filter, and to increase the scrubber’s performance, an electrostatic furnace/AC pre-filter must be used! For filters, I use 3M’s Filtrete 1250’s, and The Web (brand name) Electrostatic Replacement Pad for furnaces and AC filters. 3M quotes the 1250 to be 90% efficient with particles 3-10 microns in size. The Web filter, if washed regularly, is quoted as being able to last 5 years. To test the filter’s ability, I stacked up three filters into my 1000 CFM scrubber – two 3M 1250’s and one pre-filter. The unit was then run all day for 2 solid weeks under normal shop conditions (cabinet saws, planers, jointers, hand & machine sanding, etc… a cyclone dust collection system is also used for all machine work.) At the end of two weeks, I removed the filters. The pre-filter was completely covered and the first 1250 was as well to a slightly lesser extent. The third filter, to the naked eye, was a clean as it was straight out of the package!
Now it’s time to build!! You will have to determine the cutting dimensions of the plywood based upon the height and width of the blower, and the filters that you’ve chosen. The height of the box should give an inch+ of clearance over the top of the blower, and enough space at the bottom to accommodate the metal mounting flanges of the exhaust port(s). Because the blower’s air inlet port is only on one side, the blower will be mounted slightly off center in the box by a few inches to give air clearance. The length of the box should be 3″-5″ longer than the longest side of the filter – measuring from the filter to where the blower starts inside the box. (ex. 20″ filter: 25″ from filter to blower). If you choose pocket filters, be sure that the box is long enough so that the pockets aren’t touching the blower unit.
Once you have cut the plywood to the dimensions that you determined, locate where the blower’s flanges will be on the end board, and cut an exhaust port with a jig saw. Cut to the inside dimension of the exhaust port opening, not the outside edge of the flange – if you do, there will be a big hole with nothing to bolt the flange on to!!
Before screwing the side panels together, measure the thickness of the filter stack, and then nail or screw some cleats onto the end opposite the blower, whatever that measurement is, from the end. (This is what the filters will rest against.) You will also want to wire and mount your switch before all four sides are attached. This is where a spring wound timer could be installed. To keep the filters in place, I’ve stretched some copper wire (salvaged by my shop’s electrician across the end of the box – Any thin string will do.
The wiring of the switch and motor is very simple, but is somewhat different depending on what kind of switch you choose (timer, toggle, pull chain, etc…) I would recommend looking up a diagram in any basic home maintenance book for wiring a switch. (This can be found in the big orange book from Home Depot.) (If you have any questions, e-mail me, and I’ll e-mail you back with a diagram of how I wired some of the units that I’ve built.)
Wireless 115 V. remote switches are available at Radio Shack for $25. They also have ones with three channels.
Screw the box together, maybe throw some caulk (or phenoseal) around any seams to prevent air leaks, stick some foam gasket on the cleat so the filter has a good seal – and your off to the races!!
Air scrubber units can be hung from brackets or chains on the ceiling or joists, mounted on casters to roll around the shop, or, if it’s small enough can be placed on a bench top for smaller projects.
If you have any questions, or need a diagram of some of the things I’ve mentioned, e-mail me and I’ll supply you with what’s needed.
Dan Kornfeld, Owner/President – Odyssey Wood Design, Inc.
Replies
Dan, thanks for the detailed explanation. I've been working one of these over in my head for awhile. I've got a squirel-cage blower from an air handler unit that I'll use. This was just enough to get me moving on this project.
I've always noticed that you are willing and extremely helpful whenever somebodyhas posed a question.
Thanks alot, Hugh
A Photo of a finished scrubber would be very helpful...are you capable of posting one?
Ron,
My digital camera managed to accompany my sister-in-law on vacation! I'll can scan my original design and e-mail it to you. They are color, and show a front, side, and cutaway view of the units.
Is there a specific style of unit that you may be considering? (e.g. small/portable workbench top, ceiling or joist, or a rolling floor model.) I'm just about to finish a double ended model (filters on opposite ends), into which I'll drop a salvaged Dayton Mfg. single motor / double fan blower (looks like an oversized bench grinder). Let me know so I can send the appropriate picture.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Thats Dan for the great post. I printed this this morning at work. You got more than one of us thunking again. I've been using a 20/20 furnance filter duct taped to a box fan. A little more effort may help more, huh.
Enjoy, Roy
Edited 4/9/2003 1:14:41 PM ET by ROY_INMD
Yes to all the designs you mentioned. Seriously, I've got about 20 blower motors stored away in the shop and I'd like to put them to good use for me and my friends.
I got the motors at a garage sale. A Farmer was going out of business!!
If it's too much trouble to scan all the photos, maybe you can mail them to me?
Ron Magliocco, 1747 Jennings Road, Fairfield, CT, 06824.
Thanks again...this is just the project I've been looking for.
For those folks that cannot find a furnace blower motor and fan, I read somewhere of a fellow that bought an electric attic exhaust fan and made a similar filter network as you described. He just mounted the fan assembly on top of the box which allowed for drawing air throughout the side mounted filters then out the top through the fan. Simple and effective.
Roger
Roger,
The attic fan will work, but because it is meant to exhaust the air from an entire house, it's overkill for a box-style unit.
On the other hand, I've built whole-shop air scrubbing systems using an attic fan. I ran HVAC duct work along the ceiling with a downward facing hoods over areas where the dust might originate (e.g. oscillating spindle sander). The duct work ran back to the attic fan which was mounted into a wooden frame built into a window. A filter box was installed in the ducting 4' prior to the fan. I built the box to hold a series of filters (multiple layers for better filtration).
It works almost too well. Not only does it pull the dust right out of the air - in the winter it exhaust my nice warm shop air out the window as well! I use my shop built air scrubbers of various designs and sizes to great effect. Plus it keeps the warm air in, and noise level down!
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Take a look at this-- the guy starts with a motor and makes a squirrel
cage blower from scratch! http://www.leestyron.com/html/dustcollector.html
T
I did something similar with a friend in his shop. (Kids, don't try this at home.) When he was building the fan and vanes, I made a point of telling him that he should weigh and balance each component, and weld them to the fan plate if possible. At 3,500 RPM, you might run into problems if everything isn't just so. Did he listen? Well, the exploding fan shroud and flying shrapnel tells me that his mind might have been elsewhere!Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
I was at the dump the other day and a perfectly good squirrel cage
blower was sitting in the recycle pile, motor, mounts, wire and all.
I brought it home and plugged it in and it works great.
I thought I would need to put on a motor, but I was wrong.
A little cleaning and it will be perfect.
You never know what will come your way if you keep your eyes open.
About a month or 2 ago, I mentioned to someone I was looking for a fan for a spray booth I plan to build this summer.
He called me a few days later and had an explosion proof 24" fan for
me for free from someplace. No charge, wow.
A $300 or $400 freebee.
Like I said, you never know.
Now if I could get a free extension to my shop it would be great.
Jeff
Scored 2 squirrel cages Saturday at the dump. Only problem is they both have 230v motors attached to them and my home shop is not equipped to run them (I think). The motors have 5/8" x 6" shafts and all the motors I have are 1/2" bore x 2". Do you have any sources for Shaft extensions?
Ron,
Excellent recycling. Instead of mounting shaft extensions, it may be easier to mount a sheave on the arbors of the blower and your motor, and connect the two via a rubber V-belt.
If shaft extensions better suit the situation, McMaster-Carr (http://www.mcmaster.com) has what you'll need. Look up Shaft Collars and Shaft Couplings on their home page under Power Transmission.
Reid Tool Supply (http://www.reidtool.com) also carries Shaft Collars and Shaft Couplings listed under Power Transmission, Bearings and Linear Motion.
It is also possible to utilize one motor to drive a series of blower fans, by connecting them with a series of pulleys and belts (ex. a triple pulley on the motor's arbor, and double pulleys on the arbors of the blowers.) Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
A better scrounging way to build an air filter(scrubber) is to go to any heating company and ask for a used furnace squirrel cage blower. Furnaces are replaced because the heat exchanger fails. The blower is almost always in good shape and are dumped. Many furnace companies will let you dismantle the blower just because you need one. Even the smallest blower is large enough for most shops and run on 110 volts. Beyond that get a bag filter and a prefilter from Penn State industries. The bag filter collects down to 1 or 2 microns. The prefilter gets out the bigger pieces and is washable. Then build a large enough plywood case to hold the parts. Include a gate to allow removal and replacement of the filters. I timer switch allows the filter to continue to run after you leave the shop. Mount the filter under the ceiling along a wall near the center of the wall length. There is little if any dust on my car in the garage with my power tools and the filter when all are running. It works. Contact me at [email protected]
How is "A ...scrounging way to build an air filter(scrubber) is to go to any heating company and ask for a used furnace squirrel cage blower." different from "The blowers that I currently have operating in my shop were salvaged from large home furnaces, "
I agree with you about the bag filters, they are great, but Jackie's method of layers filters seems to work just as well and keeps the "lower profile" if that's what the user seeks.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
air scrubber cabinet
I have a perfect cart on wheels this would work for. Does it'd matter what side of box intake is on? The end is not big enough for the filter size I would like, but the side is ok.
Wiring
Would you mind sending me a copy of the wiring diagram? Thank you! I found an old furnace blower. [email protected].
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