Filtering Shop Air

Dust collection for your machinery isn't a complete solution. There are reasons to have air filtering for fine dust in the shop air, as well.June 15, 2014

Question (WOODWEB Member) :
I have a good sized home shop occupying 3/4 of the basement (1350 square ft.). Three of us work five days a week here. Two floors up from the shop, if you leave it alone for a week, you can wipe a bureau in my bedroom with a finger and see the fine particles that have settled (my wife reminds me almost daily). I have a centralized dust collection system (two 7' bags/ 3hp) but it's difficult. The printer and fax in my office (walled-off but right next to the shop) won't pull paper through the feed because the rubber capstans keep getting coated with talcum powder sized particles.

I'm going to look at a ceiling mount or roll around floor unit air cleaner (Grizzly has a number of sizes) and hook up a timer based switch so it goes on for 15 minutes every hour or so (I can leave it running when we're really kicking up the stuff) and include one of the smaller micron filters for the super fine material. If I estimate the cubic footage of my place, I get 9,450. How many cfm's in an air filtering machine would you guys recommend? I have to start doing something about this problem. I'm spending too much time vacuuming upstairs.

Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor H:
Filtering air gets more expensive as it gets more effective. The worst dust for your lungs is the finest stuff, which bag filters tend to blow all over the place. If you're cutting man made materials or sheet goods, that's plastic dust as well as wood dust that you are putting into your house. A central vac exhausted to the outside would allow you to clean the house and not re-circulate the dust. The same idea would work in the shop. I do this so it can be done.

From contributor F:
This is something that is often overlooked in shops. Guys think just because they have good dust collection they're all set - wrong. No matter what youíre going to make dust, there's no way around it. When you pick that board off the rack you've just stirred up residual dust before you even turn a machine on! The other misconception is that if you can't see dust in the air youíre all set - wrong again. The worst dust is the dust you can't see. It's the stuff that if you have a window with bright sunshine coming in you'll see floating in the air.

I have a 2k square foot shop with three air filters. One goes on every morning and runs until the lights go out. The other two get used when I'm actually working on the equipment really making dust. It definitely helps, but it's a never ending battle. I highly recommend getting the air filter and run it all day. I like the ceiling mounts as they have unrestricted air flow, but whatever works for you.

Also remember that when youíre back into your house your clothes hair and shoes are covered in dust - even if youíre careful about blowing off at the end of the day. That fine stuff is darned near impossible to separate when youíre working in the same structure.

From the original questioner:
I think I'll go with the ceiling mount AF and get a tool activated vac for the random orbital, biscuit joiner and router. I have to talk to the boys about dusting off (wiping shoes too) before going back upstairs. Now, if you guys will just lend me a couple hundred (seven-eight will do it), I can get right on this!

From Curt Corum, forum technical advisor:
When dealing with general ventilation you are trying to achieve an air change every so many minutes. The recommended air change for a factory is every 5-10 minutes. Letís say we use seven minutes. 9,450 cubes divided by seven minute air change is 1,350 cfm. Also, if you use a ceiling mounted unit it is best to have it on a side wall in the middle. This will create a circular motion of the air. Some other air change examples are: Restrooms - every five-ten minutes, Plating rooms - every one-five minutes and Foundries every two-eight minutes.

From the original questioner:
Thanks, Curt. That was (amongst a good overall discussion) the info I was looking for. Grizzly has a remote operated, timer included, ceiling unit that does 1400 cfm for $295. I'm assuming the seven minute example is a decent standard for a small (but busy) place like mine. While I'm at it, do you suggest the one micron filter to go with it? Can I simply clean it/blow it out from behind (outside, of course)? They're a bit pricey.

From Curt Corum, forum technical advisor:
I would definitely get the one micron filter option. Grizzly claims you can even wash it. As far as the volume of air, I used seven minute air change in one of our departments where a lot of hand grinding is done on metal parts. I cannot achieve a good pick up at the source. Air quality is tremendously better. When we did our first primary filter change it was amazing as to the weight of the filter. The filter must have weighed ten pounds with all the fine steel grinding dust embedded. We purchased our unit from Airflow Systems in Dallas Texas.

From the original questioner:
To think that wood, if in a small enough particle form will suspend in air for quite a while is interesting info. To think that that can be true of metal particles - holy mackerel. I would have put money down that that wasn't true.

From contributor D:
I am assuming you have separate HVAC for the shop and home. If not you must separate them and seal any and all openings between the two. An airtight door is also necessary. Any time you go from shop to home use an outside entrance, or change clothes in the shop as any opening the connecting door lets dust into the home.

Finally, install a one micron or better air filter so as to blow clean filtered air out of the shop into the home so the home has a slight positive pressure. This may sound like overkill but how serious are you? The positive pressure in the home will stop dust coming up the holes you missed sealing, you can't find them all.

From contributor Z:
Note: you do not want to use PVC for any ducting installation. It creates a static charge and could explode unless grounded properly. The same thing goes with shop vacs.

From the original questioner:
Contributor D - I like the idea of mounting one air cleaner whose filter side faces the shop and whose outflow goes to my office (sitting adjacent). That might offset the fact that dust comes out of the shop trying to rise upstairs from heat rising and the fact that I have a fireplace and a wood burning stove upstairs that are always looking to replace the air they draw in and send up their chimneys.

Contributor F - all my ceiling hung hoses have a grounded wire running through them for that very reason.