How large or how many filters - air filtration

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Forum topic by SnowFrog posted 07-12-2011 06:42 PM 1499 views 0 times favorited 6 replies Add to Favorites Watch
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102 posts in 2746 days

07-12-2011 06:42 PM

Topic tags/keywords: air filtration question

Hi there, I am in need of some advice.

I have a tiny shop (~150sqft) in parts of my finished basement. It’s been a little over a year now that I had to give up my garage shop ;-( so now Dust in the air is very much an issue. Not only for my lungs but for everyone elses and the dust all over the basement.

So I have been thinking about building my own air filtration system based on commonly available filter sizes (14×20, 16×25). I got a blower at the market a few weeks back for $10. My guess is about 500-700 cfm, so more than plenty for my small room.

As I have been going through old post it looks like some configuration require very frequent filter change. I know this is a good thing cause it means they are cleaning a lot of stuff that would otherwise end up in your lungs but being a procrastinator for this type of things, I was thinking about putting infeed filters at both ends of the box, thus doubling the effective filter size and having to change them 1/2 has often!

But it occured to me, that I would also decrease the static pressure over the filter area, that is, loosing 1/2 the air flow per sq in, would it be enough to suck in the dust effectively. So with my little 500-700 cfm blower, should I stick with one 16×25 infeed or could I go to two 16×25 openings.

By the way, the outfeed will actually be blown outside during the summer and recirculated to the next room during the winter months. This will create a negative pressure in the room and keep the dust in the shop as much as possible.

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

6 replies so far

View lew's profile


12428 posts in 3955 days

#1 posted 07-13-2011 02:55 AM

I have almost exactly what you are suggesting- except it is permanently exhausted to the outside. It is a furnace blower (squirrel cage blower) mounted in a box that has an opening on both ends. I made some “tracks” to hold furnace filters over the holes. These traps the dust before it gets to the motor. Also put a 1/4” wire mesh screen over the holes to prevent the suction from pulling the filters into the blower. A word of caution- from personal experience- this set up is powerful enough to pull furnace exhaust fumes DOWN the chimney and into the basement.

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View Grandpa's profile


3261 posts in 2875 days

#2 posted 07-13-2011 03:05 AM

If you are blowing the air outdoors, why have a filter? you are cleaning the air in your shop and getting rid of it. Of course I live in SW Oklahoma and the wind blows constantly so a little dust is not even noticeable. I think a person should buy a good filter from Grizzly or Penn State or anyone that markets a good filter (.5 micron or something like that) and make his blower work on that. Then buy regular furnace filters and put it in the line first to keep the better filter as clean as possible. Then discharge the air back into the shop. You could use 2 of the good filters inside if you wanted. In my ACE hardware store the filters all cost the same price whether they are 20×20 or 30×30. The larger filter should still work just as well. You are going to restrict it right away anyway.

View auggy53's profile


159 posts in 2880 days

#3 posted 07-13-2011 06:44 AM

i have a smaller shop im my basement for winter time 12×20 .i took a window a.c. unit and ripped it apart to get to the 2 fans ,motor and mounts and built an mdf box around it with a filter on each end . stacked the filter with the mornal fiberglass and on top of that i use a coarser washable filter and helps with filter cost . actually it works so good i have to clean it twice a day.

-- rick

View MedicKen's profile


1615 posts in 3662 days

#4 posted 07-13-2011 07:04 AM

There is a really good book that covers this subject as well as overall dust collection by Sandor Nagyzslancy, Shop Dust Collection, I believe. In the book it covers dust scrubbers and a mathematical equation on how to properly size the scrubber. I found the book to be a very good reference and a must read for anyone setting up dust collection. If you cant buy it locally take a look at your local library.

-- My job is to give my kids things to discuss with their

View hairy's profile


2782 posts in 3732 days

#5 posted 07-13-2011 01:37 PM

I have a homemade air cleaner, and a commercial one.

Along with a good dust collector, I have the dust mostly under control. These 3 get the majority, but I still need to use a vacuum cleaner . I take dust control serious when it’s inside the house.

-- My reality check bounced...

View SnowFrog's profile


102 posts in 2746 days

#6 posted 07-13-2011 06:59 PM

Thank you guys for the advise!

Lew – Thank for the word of caution. The main heating is electric but I do have a fireplace upstairs so i’ll have to pay attention.

Grandpa – Even if I vent outside, I would have to add filters first to protect the motor but, to vent outside I am using an old Jen-air cooktop vent, that vents directly under our deck so I would not want to see what I am venting out comeback through the patio door. The main difference between when I would vent outside or inside would be the type of filter I would use. I would likely add an HEPA as an outfeed when I vent in the otherside of the basement.

auggy53 – thanks for the pics – obviously amazingly efficient, hpe mine works as well.

Medicken – Thanks will look into it, but what I keep reading give me a lot of confidence!

hairy – I only have a shopvac so far. So this is a start for me, my next stop will be to beef-up my shop vac with a cyclone chip collector of some sort.

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

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