# Workshop air filter



## Andrew714 (Nov 28, 2014)

Hello,

I am planning on building a shop air filter, but I'm trying to figure out what CFM I can put through standard pleated furnace filters. I'm planning on building a ceiling mounted box with a 12"x24"x1" filter on each side, and a fan on the bottom, which I think moves about 1000 CFM or just under that. Does anyone have any thoughts about whether these filters are large enough to accommodate the airflow, or should I use bigger filters?

Thanks,

Andrew


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## PPK (Mar 8, 2016)

1000 CFM is probably a little on the high side for that size of filter… They may blow out or kind of come apart unless you have some sort of screen to help stiffen them up. Another concern is the Merv rating of the filters. The higher the Merv (better filters that catch more/smaller dust) rating, the harder it will be to force air through the filter. They'll also plug faster.

I made a shop air filter with 16×20 filters and a small squirrel cage blower a long time ago. It worked OK. For what it costs nowadays for a air cleaner, I'd just buy one. That's my opinion anyway.

Here's one that's got decent reviews before hand. At the least, it could be a good guide for your specs if you make one of your own.

https://www.amazon.com/WEN-3410-3-Speed-Remote-Controlled-Filtration/dp/B00LPD9BDI


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## woodbutcherbynight (Oct 21, 2011)

The WEN unit is a good unit and works well. Have had mine for 3 years.


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## them700project (Aug 12, 2015)

The grizzly is another choice and has interchangable filters with the wen


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## sansoo22 (May 7, 2019)

I'm torn 50/50 on the build vs buy side of this. I have lots of home automation running and building an air cleaner lets me tell Google or use my phone to turn it on or off. Or get fancy and turn it off 10 minutes after a shop motion detector hasn't detected any motion. I also feel the DIY approach lends itself better to an air cleaner cart vs ceiling mount. There is a Jay Bates vid that uses a cart style cleaner as a planer cart which to me makes a lot of sense. In his 400 sq ft space the air cleaner being lower did a remarkable job. Something about the direction the squirrel cage directs air kept the air in the shop better than outside.

For ceiling mount i lean towards PPK's opinion of just buy one and hook it up. Unless of course you want to do some fun automation with it and then you need something with smart controls or you have to DIY and have it hooked to a smart switch.


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## LesB (Dec 21, 2008)

I made a mobile cabinet air cleaner and used an old house air handler blowerin it. It has a filter on one side (25×25) but double up with two 1" thick filters. The outside filter is the coarse fiberglass and the inner is a merv rated filter. No filter on the exhaust side.
The portability allows me to locate it near the dusty work (sanding) or position it so it circulates the heat from my wood stove. The top of the cabinet I use for my power sharpening station. The only time I think I would need some sort of electronic gadgets to turn it on and off is when I let it run for a few hours to clean the air before I do any finishing work. Had it for 20 years and works great. 
Expenses, one recycled furnace blower (usually free from a heating contractor) and a sheet of plywood plus wheels.


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## sansoo22 (May 7, 2019)

> I made a mobile cabinet air cleaner and used an old house air handler blowerin it. It has a filter on one side (25×25) but double up with two 1" thick filters. The outside filter is the coarse fiberglass and the inner is a merv rated filter. No filter on the exhaust side.
> The portability allows me to locate it near the dusty work (sanding) or position it so it circulates the heat from my wood stove. The top of the cabinet I use for my power sharpening station. The only time I think I would need some sort of electronic gadgets to turn it on and off is when I let it run for a few hours to clean the air before I do any finishing work. Had it for 20 years and works great.
> Expenses, one recycled furnace blower (usually free from a heating contractor) and a sheet of plywood plus wheels.
> 
> - LesB


That's basically the idea I had for one. Maybe put something that causes lots of dust on it like an oscillating spindle sander. The fancy gadgets are of course a luxury but since i already run a home automation server I always like to think of simple things I can hook to it just for the convenience factor.


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## ibewjon (Oct 2, 2010)

I have a web, and the three speed blower and hours to run are built in. Easy. Hang and plug in.


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## Andybb (Sep 30, 2016)

Izzy Swan says box fan moves more air.


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## Scap (Aug 7, 2018)

> Hello,
> 
> I am planning on building a shop air filter, but I m trying to figure out what CFM I can put through standard pleated furnace filters. I m planning on building a ceiling mounted box with a 12"x24"x1" filter on each side, and a fan on the bottom, which I think moves about 1000 CFM or just under that. Does anyone have any thoughts about whether these filters are large enough to accommodate the airflow, or should I use bigger filters?
> 
> ...


You can get filters that will handle 500 fpm velocity, but that won't be off the shelf at a big box store.

Get your velocity down below 300 fpm, and you should be good.

1000cfm/300fpm*144= 480sq inches of filter area.
20×24 would be more appropriate.


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## kelvancra (May 4, 2010)

I have a house filter system in mind. Some of the things I have planed for it may be applicable to your project:

1) The unit will have a manometer, on the fan side to monitor filter condition.

2) The unit will use a standard, three speed HVAC fan.

3) The unit will use two intake filters, rather than one. Since mine will be a roll around unit, I'll either have a filter on the left and right or one on top and one on the bottom.

4) The filters will be pleated 4" x 20" x 20", like the ones used on my home system. The pleated filters, just as they do on shop dust collectors, will greatly increase air flow and reduce the load on the blower.

NOTE: I can start with MERV 11 or 13 and see what I think.

5) I'll use pre-filters (e.g., washable foam) to stretch the life of the expensive, 4" filters.

6) I'll install a four position switch to allow me to take advantage of the fan's three speed (low, medium and high) and to, of course, allow me to turn it off.

NOTE: If I place the filters at the top and bottom, the cabinet only has to be as large as the fan with a couple inches on both sides of the intake to provide full flow. That's only about sixteen inches square and about 24" tall.


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## kelvancra (May 4, 2010)

I can say I doubt any box fan would move air all around a house through ducts as well as a common squirrel cage.



> Izzy Swan says box fan moves more air.
> 
> - Andybb


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## Andybb (Sep 30, 2016)

> I can say I doubt any box fan would move air all around a house through ducts as well as a common squirrel cage.
> 
> Izzy Swan says box fan moves more air.
> 
> ...


No. But a box fan will move and filter more air than a WEN or Grizzly air filter. Turn it on high and leave it on while you're working. A shut off timer is a good idea. You'll know when the filter is dirty. I have one of those WEN filters hanging from the ceiling. Even using my dust collector an hour after cutting purple heart the filter has a purple tint to it so I know it's working.


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