# DIY Air filtration blower...is this overover kill?



## beelzerob

I plan to build my own box for shop air filtration....doesn't seem to be much to it.

The shop (will) be around 38' X 12' X 8'. I calculated all that out based on a site I was learning about air filtration from, and with trying to circulate all the air on the shop 8 times, and allowing for air friction, yadda yadda, it came up with needing about a 1000 cfm blower.

I called my local HVAC guy to see if they had anything laying around to fit the bill. He's offered a "3 ton blower, (1200 cfm) or less probably, 3 speeds, 220 volt" and says I can have it if I want (they're doing around $15k worth of geothermal work on my house, so he can probably afford to just let this go). All of the DIY setups I'd seen, you build a box and put the blowers in it and filters on it and suspend it from the ceiling. I think what he's offering me is a furnace blower, which is going to be pretty big I think, and probably wouldn't make sense hanging from the ceiling...I'd have to put it in the corner and duct to it probably.

Is that thing overkill you think? If I go with that, then I'm going to have to wait for the 220 to be wired in before I can build a box around it, whereas if I waited for a 120v, I can build it and use it now just from local outlets.


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## woodnthings

*Free is free...*

But 120 V, 3 speed blowers can be had for $40.00 or so as I got mine.
Usually furnace repairs companies change out a furnace and the blower is still serviceable.
I personally would not use a 220V only blower. Takes up space in the panel and just not necessary. JMO bill
Blower capacities seems OK though. 1000 cu ft per minute is about right at high speed on Jet units.

If at all possible, build your shop with a 10 foot ceiling to allow for 4X8 panel movement. Been there done that with an 8 foot ceiling height! PITA....:furious: bill


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## beelzerob

Well, he indicated I could hold out for a 120v blower too if I wanted...he just didn't know when those might be available. I guess it makes sense to wait since with a 220v blower I wouldn't be able to do anything with it in the near term anyway...it'd just sit there.

Where did you get your 120v 3 speed blower for only $40? As in, what sources should I be looking at? Craigslist doesn't have that very often here.

I am going to an auction this weekend where they show a 1/2 hp motor/blower...but I have no idea what that would convert to for CFM. Maybe for $10 it'd be worth having....




woodnthings said:


> If at all possible, build your shop with a 10 foot ceiling to allow for 4X8 panel movement. Been there done that with an 8 foot ceiling height! PITA....:furious: bill


Heh...well, the wife probably wouldn't appreciate me removing the first floor floor to do that.  The shop is in the basement, and at least we had the sense to have 9' ceilings down there. The ceiling will be closer to 9' than 8' actually, I just allowed for various obstacles that might be in the way.


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## Chippin-in

Is it possible for someone to post pics of their homemade air filtration system? I am more inclined to make my own than pay what a new one costs. Thanks


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## beelzerob

I can't seem to find the link now, but I have bookmarked at home a great site where a guy built 2 of his own air filtration units. It's very helpful and informative (though one of his formulas for how much CFM you need is wrong). I'll post it when I get home.


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## woodnthings

*Try your local furnace repair*

Either an independent business man, owner operator or if you see a repair truck parked along side the road or at Home Depot ask the guy what he would have. A personal contact is always better than a phone call in my experience. In my case I had a friend who had a friend...
If you can't use your friends...what good are they? :blink: bill

BTW there is a certain amout of science to this project, filter types and mircon size, as these links discuss. As the saying goes anything is better than nothing , but a 1 micron is better than a 5 micron filter.

Just an aside, I was using my shop vac to clean the shop floor and couldn't understand why I smelled so much dust and could see it coming out the exhaust port??? So I lifted off the motor unit only to find the filter holder had dropped off the bottom as was sitting on the bottom. I wonder how much dust I inhaled from that...... 


Some links: http://www.woodworkingtalk.com/f27/diy-air-cleaner-filter-12336/
http://www.woodworkingtalk.com/f12/hf-air-filter-system-any-good-11475/

http://www.liwoodworkers.org/downloads/Dust%20Collection%20&%20Air%20Filtration.pdf

Bob Willing gunrackguy 
Join Date: Jul 2008
Location: UP of Michigan
Posts: 211 







*Air Filtration* 
This is the air filtration I made for my shop. I purchased the blower motor used from a heating and ventilation shop locally for $50.00. The trick is to make sure that the filters are about 3" away from the blower housing so that the air is filtered across the entire filter. You can put whatever filter grade you want or willing to pay for into the filter. Mine has two 16 X 20 filters. I made the unit size to fit the blower motor housing. This blower has four speeds and if I want to change speeds I remove one of the filters and simply insert the connector into an alternate spade. Nothing fancy but it does the job, yes it is noisy but the air movement cools off my shop. You could vent it out side. The track that holds the filters in place are siding "J" channels. 
Attached Thumbnails


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## Chippin-in

And so now I ask these questions: 

Where is the best place to position this system? 
The center of the shop or at one end? 
Does the shape of your shop dictate the position (square or rectangular)? 
Or does it matter? 
I see they use electrostatic filters on the infeed, but what about outfeed - regular filter?

My shop is a rectangle (approx 10'x20') inside a square. Half of a 2 1/2 car garage (right now, hopefully it will grow soon :smile It has an unfinished ceiling and walls.

Are yall sorry I found this post and started asking questions? :laughing:

Thanks.


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## beelzerob

Nonsense chippin', bring it on. The more info gathered in this thread the better.

To try and answer some of your questions:

The ceiling seems a favorite place, mainly to just get it up out of the way. That's probably not going to work in my basement unless I can position it over a permanent table area (but I dont forsee having much "permanent" in my smallish area). Also, center of the room is a good place because the idea is to filter all of the air in the room, and if you put the unit in a corner of side of the room, then it's not going to get much of the air from the other side of the room (especially with a rectangular room). You could fix that by having the exhaust of the filtrated air ducted across the room.

You dont need a filter on the exhaust (outfeed) of the filtration...just on the inlet air. 


Here is the site that I found very very useful for information. He has a link about DIY air filtration that goes into pretty good detail about calculating the size unit you need and how to build the box around it.


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## amckenzie4

The "Small Shop" booklet put out by Shop Notes had plans for a DIY air filter. They used a small squirrel cage blower and three furnace filters.

For suppliers, I'd check American Science and Surplus first -- they've got a whole lot of cheap squirrel cage blowers here.

(Actually, they're about the first place I'll check for just about any random small piece for a project... their prices are good, and their selection is truly strange.)


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## beelzerob

Any idea how I'd convert HP to CFM? I've seen a pic for a "1/2 HP blower" and it shows the motor connected by belt to a squirrel cage. The pic is for an auction I'm going to soon, and for a cheap price it might be worth it, but how will I know how much CFM it can do (and thus if it's suitable for my filtering needs)?


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## mdntrdr

It would depend on RPM and blower size.

No way to calculate from HP, would be my guess.


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## woodnthings

*The commercial units have 1/6th HP*



beelzerob said:


> Any idea how I'd convert HP to CFM? I've seen a pic for a "1/2 HP blower" and it shows the motor connected by belt to a squirrel cage. The pic is for an auction I'm going to soon, and for a cheap price it might be worth it, but how will I know how much CFM it can do (and thus if it's suitable for my filtering needs)?


So, a 1/2 HP unit will be more than adequate, regardless of CFM. That may be located on a plate on the blower unit when you see it. A owner's manual for that particular furnace may also have it.  bill


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## beelzerob

woodnthings said:


> So, a 1/2 HP unit will be more than adequate, regardless of CFM. That may be located on a plate on the blower unit when you see it. A owner's manual for that particular furnace may also have it.  bill


Well, all I saw was the motor and the squirrel cage, so I doubt there will be a manual, and certainly no time to go look it up, but I'll look all over for some kind of plate with specs on it. Sounds like it'd be useful to have for a low enough price (considering the HVAC guy was going to give me a 1200 cfm blower for free!).


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## Chippin-in

I found this link for plans to build a filtration unit.

http://books.google.com/books?id=fY...result&resnum=4&ct=result#v=onepage&q&f=false


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## MariahHolt

*Here's the My air filtration box I made for my shop*

After reading these forums and shopping around this is the filtration unit I built for my shop area. The box is made with a 2"x2" frame with 1/2" plywood exterior. I had a buddy who gave me an old AC unit blower motor. Not exactly sure how large the motor is, from what I've researched I think its 3/4 HP or 1 HP. The box is 18"x24"x48", around 75lbs. Mounted from the ceiling with i-bolts. It has (2) double filters on it, (16"x20") one on bottom and one on the back. Total price for materials, around $80. One thing I did do, I used some wide peel-&-stick weather stripping against all seals making it really air tight. 

Not exactly sure the CFM, but it really moves some air! I use cheapo filters on the far outside with some expensive ones on the inter part. I can tell it's made a big difference in the air quality in my garage.


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## beelzerob

I just got the blower a couple days ago from my HVAC guy. Apparently it's multi speed, and he didn't know which wire was which, so I have to wait a bit to figure that out.

What are the 2 switches on the box?

Where is the actual blower? It seems no matter where it might be, one set of filters might be pretty close to it. I forget what the distance is, but I read somewhere that the blower should be a min distance from the filter to ensure air is pulled through the whole filter.


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## SteveEl

wood magazines "best shops" (2007 ed) showed a guy with a large shop, where he had clustered some workstations out away from the walls. Part of that cluster included a mobile cabinet/worktable, where the bottom half of the cabinte box was his shopbuilt air cleaner, and the top half was drawers. Furnace filter on front, and clean air exhaled in back.


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## MariahHolt

beelzerob said:


> I just got the blower a couple days ago from my HVAC guy. Apparently it's multi speed, and he didn't know which wire was which, so I have to wait a bit to figure that out.
> 
> What are the 2 switches on the box?
> 
> Where is the actual blower? It seems no matter where it might be, one set of filters might be pretty close to it. I forget what the distance is, but I read somewhere that the blower should be a min distance from the filter to ensure air is pulled through the whole filter.


 
Yea it’s got 2 switches on it. One is for the on/off for the blower. The other is just there wired to nothing. It’s just there as a reserve, I don’t know what exactly I wanted to do in the future so added a second switch as a spare/extra. This blower is also a 3 speed unit, my buddy the HVAC guy wired it on high. You can put on a 3 speed switch on it to utilize all those speeds. I was looking for the simple route on this setup. On mine the blower is located there where the switch is. I was concerned that if I just had 1 air inlet that the suction from the blower would tear up the filters over time. The blower blows the air towards a wall, its summer right now so I’ve got the garage door open.
I’ve got a bad back, so mounting this beast became rather a challenge. I found a good way to help hoist the unit up onto the ceiling using a “Gambrel and Pulley Hoist” I got from HF. (Item #99758 , best $13 I’ve spent in a long time, I’ve got a feeling I’ll be using it again.)


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## ecenur

amckenzie4 said:


> The "Small Shop" booklet put out by Shop Notes had plans for a DIY air filter. They used a small squirrel cage blower and three furnace filters.
> 
> For suppliers, I'd check American Science and Surplus first -- they've got a whole lot of cheap squirrel cage blowers here.
> 
> (Actually, they're about the first place I'll check for just about any random small piece for a project... their prices are good, and their selection is truly strange.)


I like this idea, would I be able to a purchase a furnace filter online from this site, or is there any other websites that are similar that also has reasonable prices I can order from and have it shipped to my home?


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## amckenzie4

ecenur said:


> I like this idea, would I be able to a purchase a furnace filter online from this site, or is there any other websites that are similar that also has reasonable prices I can order from and have it shipped to my home?


I'd be surprised if they have filters, but just about every big home improvement store (and a lot of small hardware stores) carry furnace filters. And I'm sure you can order them online somewhere... I just don't know where, off-hand.


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## spirit warrior

Hey guys, love all of the great ideas for shop air filtration! I also am using my garage for my wood shop when Mama is gracious enough to park outside for a few days for my current project.  My question is what is the noise level for all of these blowers? Cleaning the air and recirculating it back in the shop makes sense, but how much noise is running continually? I made a shop vac collection system using the Thien baffle design and am blown away how well it actually performs, but the fines are still present, which is why I am looking for the blower filtration ideas.


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## nkdenton

Earlier posts worried about hp and how that mapped to cfm. Here are some basic principles to keep from overthinking this. 

Two things you can keep in mind are that hp is only relevant when overcoming a lot of back pressure in a ducted system like your home AC system, and cfm just determines how quickly the air is circulated past the filter. A shop air filtration system is really only overcoming the pressure loss of the filter, which is a function of how fine it can filter and the rate at which it clogs up. If you have a lot of cfm it just wash the air in your shop out at a faster rate. The higher the cfm, the less likely you get dust settling but the noisier it will be. Of course there is a practical limit and there will be dust no matter what. 

My shop is 13' X 18' X 9' ceiling, so I have 2,106 cubic feet. One air change per hour (ach) would be 2100 cf/hr or 35cfm. I'd like to get about 8-10 ach based on some wood shop / machine shop guidelines I've seen so a 2500-3500 cfm fan will do the trick. That is what a 20" box fan moves on high so some of the poor man's filter boxes using box fans are not too far off the mark, it's just that a blade fan is less effective than a squirrel cage fan when sucking air through a filter. 

So if you can get a cheap squirrel cage fan to pull 8-10 ach through a high efficiency filter or two and a short plenum box (3' long or shorter) you will be in pretty good shape. If you go the poor man route, you'll still get filtration at about 1/2 the recommended ach but at <$20 bucks at WalMart you can't beat the price and will be better than nothing.


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