Air Cleaner/Dust Filter

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Project by Mike Merzke posted 09-25-2012 11:52 PM 8141 views 43 times favorited 13 comments Add to Favorites Watch

He is my attempt at a overhead dust filter/air cleaner. I bought a $20 box fan and a couple air filters and with some scrap wood I had laying around the shop…. here it is. Other than testing it to make sure it runs, I haven’t had a chance to see how it actually filters the dust out of the air. Guess I need to get to making some saw dust and see.

-- Mike Merzke,

13 comments so far

View  woodshaver Tony C   's profile

woodshaver Tony C

6825 posts in 3861 days

#1 posted 09-26-2012 12:14 AM

Every shop needs some kind of dust fillter.
They do work! But It’s hard to get all the dust.
I made one for my daughters bird room to collect the dander. I used the same fan but a different fillter. You can see it here.
I like your idea of hanging up out of the way! Looks good!

-- St Augustine FL, Experience is the sum of our mistakes!

View CueballRosendaul's profile


484 posts in 2648 days

#2 posted 09-26-2012 01:16 AM

I’m not sure how much my opinion is worth because my shop is pretty dusty except the day after I blow it out the door with a leaf blower. However, I do a lot of air flow testing and pressure balancing and have learned a few key things that may dramatically improve your collector effectiveness. I have also been to some pretty intense training sessions for industrial ventilation.

First, you should install something on top to direct the filtered air out in a stream over the ceiling. A slotted return register grill with the slanted louvers would work, or you could build an inverted curved or angled piece to mount on top of the fan or on the ceiling.

Second, a slightly wider frame around the face, not to shrink the opening, but to keep the fan from “short circulating” where it pulls the air that was just exhausted out the top back into the opening on the bottom. You want it to pull new dirty air, not the just filtered air. I just looked up the numbers in my Industrial Ventilation Manual of Recommended Practices, and if you had about a 6” lip around it, you’d collect 30% more air from underneath because the lip would be blocking the air that comes out of the top from coming back into the bottom.

Think of the air as if it was water. By spraying it up at the ceiling, your going to get a lot of it right back in the same spot. Also, turbulence is bad and takes away from effective circulation, manage the flow.

As a last note, I’m a big fan of spot filtering for sanding and finishing. I built a portable downdraft table that keeps the dust from getting airborne in the first place. Its not 100% effective however, so I’m also a believer in filter units like yours.

Hope all this helps.

-- Matt CueBall Rosendaul. I don't think I've ever had a cup of coffee that didn't have cat hair or sawdust in it.

View Brianb1's profile


82 posts in 2670 days

#3 posted 09-26-2012 01:29 AM

I found my project for the weekend !! thanks for sharing !!

View Arnies's profile


126 posts in 3016 days

#4 posted 09-26-2012 09:06 AM

Good Idea Mike and cost effective.

-- arnies

View padric's profile


34 posts in 2740 days

#5 posted 09-26-2012 09:56 AM

Good use of project time. I’ve built a filter like this but have it on wheels so I can position it in different parts of the shop near the dust generation. I use a timer switch so that it continues to run for awhile after I leave the shop. I also use a downdraft box hooked to a portable vacuum . This seems to do a better job, with a HEPTA filter, on fine dust generated with random orbit sanders.

-- [email protected]

View mondak's profile


71 posts in 2909 days

#6 posted 09-26-2012 12:56 PM

I also have a downdraft table for sanding and/or just letting it run to clear the shop air. I have 2 stacks of 3 filters with the lower filters being 13 merv. These catch the fine dust that the 2 upper filters miss.
I would suggest to anyone with an air filtration system to find filters with at least 13 merv. There is no sense in recirculating dust if you can help it.

View Sawdustmaker's profile


295 posts in 4305 days

#7 posted 09-26-2012 02:49 PM

In addition to my dust collector and I am sanding making fine particles of dust for an extended period, I run our old rainbow vacuum cleaner. For those of you who have never seen a rainbow, they use water and not a filter to collect the dirt it vacuums up. When the sun comes through the window it is easy to see particulates in the air. If I run the rainbow for about 10 minutes after I blow down the shop, there is virtually no dust floating in the air. When I’m finished, I just dump out the dirty water down the toilet.

-- Brian, Virginia Beach

View SnowFrog's profile


102 posts in 3055 days

#8 posted 09-26-2012 03:02 PM

Excellent Idea. I amin th process of building a dust filtration also.

I have a questions for cueballrosendaul, since you seem to know a think or two about ventilation. I sometime see people stacking 2 to3 filters of various rating one after the other from lower to higher grade (Merv rating). Does this actually filter better or simply extend the life of the higher grade filter?

-- One can dream, about a passion not yet fully fulfilled!

View CueballRosendaul's profile


484 posts in 2648 days

#9 posted 09-26-2012 04:30 PM

Snowfrog, a pre-filter is a good idea, but probably not neccessary or effective. Sawdust is 30 microns or larger. We can visually see starting at about 40 microns in size. A MERV 4 filter is all that is necessary to collect such particles. If you want to capture aerosolized finish particles, you might need to get up to a MERV 8. Beyond that your trying to capture such small particles that you’ll be reducing the air-flow by having too much filter. HEPA is absolute overkill and counterproductive. Most of the cheap blue fiberglass filters are MERV 1 which the sawdust particles will just go through. If they’re big enough to be stopped by that cheap filter, they won’t be airborne, so for a downdraft table, or a horizontal collector might be fine but would be plugging up all the time. A MERV 4 pleated 2” or 4” would be perfect.

-- Matt CueBall Rosendaul. I don't think I've ever had a cup of coffee that didn't have cat hair or sawdust in it.

View SnowFrog's profile


102 posts in 3055 days

#10 posted 10-02-2012 01:10 AM

CueballRosendaul – Thank for your answer and specially those links. It is nice to actually see some numbers. There is a lot of noise out there about needing super good filtration HEPA and DC with better than micro level. It is hard to actually know what is truely needed.

From the link you provided with saw dust being 30 micron it validates completely all those folks who have simple rigs without the fancy 2-3 stage filtration etc…. The one I am trying to put together will use simply a 3M filtreete 1000 which I belive is about a mirv 11. Those are common and cheap.

Any recommendation as to the blower size (CFM) some say. Some say replace the air in your shop 6 to 10 times. an hour and that is excellent.

Also a more pointy question. Is there a ratio to maintain between the blower size (CFM) and the actual size of the filter. At the extreme a mini fan with a gigantic filter would not pull anything or the opposite, a mega blower with a tiny filter may simply impart so much speed to the particules in suspension that they may blow through the filter material. Any comment?

-- One can dream, about a passion not yet fully fulfilled!

View CueballRosendaul's profile


484 posts in 2648 days

#11 posted 10-02-2012 02:56 AM

Selecting the blower motor for the fan is more a function of noise, energy use, and durability. A nice quiet motor will be used much more than a noisy annoying one. The best set up would be a continuous duty motor that is outside the path of the dust, that’s why squirrel cage or belt driven fans are better than a typical fan motor with blades attached. Keep in mind that all the typical motors you will use will need a few drops of oil on a regular basis to keep them from seizing up, so make sure if the motor has an oil port its accessible with disassembling the collector or turning it upside down Dust collecting on the coils of the motor windings will also add to the possibility of overheating (many motors have a thermal overload that shuts it down if it gets too hot). On a regular basis, when cleaning the filter, give the motor a good hose down with the air compressor. I do this to my table saw and sanders and can’t believe the dust that comes out of the motor. As for filter and cfm sizing, you might have a tough time calculating the cfm needed or achieved. Keep in mind that a pleated filter is a huge surface area.

-- Matt CueBall Rosendaul. I don't think I've ever had a cup of coffee that didn't have cat hair or sawdust in it.

View sparky52tx's profile


36 posts in 3026 days

#12 posted 10-06-2012 09:48 AM

Great idea! I will use this in my shop probably the same way you did using the garage door plug.

View Roger's profile


21011 posts in 3312 days

#13 posted 06-18-2014 01:08 AM

This version is a whole bunch better than the one I had. I used a box fan with filters on the in and out sides of it in my ceiling for a few years. I would sweep out the filters whenever they needed it. It worked very well. I think anything you can do to combat that nasty dust, you will be further ahead, and be healthy much longer than just breathing that nasty stuff. I will get around to making a little better one since I have acquired a squirrel cage, and such to put together one.

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed. [email protected]

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