Air Filtration!

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Forum topic by jaysonic posted 09-13-2012 01:55 AM 2164 views 0 times favorited 24 replies Add to Favorites Watch
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219 posts in 2167 days

09-13-2012 01:55 AM

So, I’ve recently discovered that I’m allergic to all wood airborne particles. What a downer. I’ve been working in my shop with a real skookum dust mask for the last few months, but I’ve decided I want something more. I’m getting an electrician to re-wire my shop so that I don’t blow breakers when using two tools on one outlet, like a shop vac and TS. I also have a wonderful blower, really loud, but boy does it move air. I’ve noticed that with this blower on, I don’t even need a dust mask to avoid the allergic reaction, although I still wear it when doing tasks that really put out dust. However, I now really want to BUILD an air filter. This way,with the combination of, shop vac hooked up to my tools, dust mask, and blower, I can now have an air filter that runs while I’m working, as well as afterwards to really help keep it cleaner. NOW: to my question:

I’ve been reading a lot on air filtration systems, but I thought I’d ask fellow LJ’s their advice. What is the best way to construct one? My sisters boyfriend is an HVAC man, and he’s now started looking out for a fan for me. Would a furnace fan work best? How many filters do I use? Pre-filter, post-filter? Rubber gasket seals? I’d like to hear anything and everything from anyone and everyone, haha. Maybe even a little help on the design itself.

I’ve never made an air filter, and, since I’m allergic to wood…I don’t want to have to do this more than once, I want it to work right the first time. So, thanks in advance for all your help!!


24 replies so far

View SSG's profile


39 posts in 2108 days

#1 posted 09-13-2012 02:02 AM

They discuss this issue in a very old issue of Wood magazine, they built a box out of plywood and use a squirrel cage blower. If you use a pre filter with a Merv 13 filter it would work best. I just moved I will have to look for the thing and get back to you.

View nwbusa's profile


1021 posts in 2311 days

#2 posted 09-13-2012 02:12 AM

You used “skookum” in your post and have therefore been positively identified as Canadian :)

-- John, BC, Canada

View jaysonic's profile


219 posts in 2167 days

#3 posted 09-13-2012 02:23 AM

Wow, thanks SSG, that would be really helpful.

Haha, thanks John. Van. Isl, BC.

View Grandpa's profile


3259 posts in 2700 days

#4 posted 09-13-2012 02:37 AM

I think if you use a squirrel cage style fan you will want the filtration on the suction side. I personally would look into some of the filters used on commercial units then use a prefilter that you buy locally off like a furnace filter. The second filter is the one that will collect the fine particles and those are the bad guys. The primary filter will keep the secondary filters cleaner. Those filters should collect the very finest particles. Look at some web sites of different companies and see what you find. If you use a fan then you usually put the filters on the discharge side of the fan.

View OnlyJustME's profile


1562 posts in 2402 days

#5 posted 09-13-2012 02:52 AM

You can watch this guys youtube videos
I made one using a multi-speed air handler/furnace fan to create a negative air pressure during a kitchen remodel so dust didnt get all over the house and it really moved a lot of air. Enough to keep pulling down the plastic sheeting on the doorways. It sat on the floor and resembled one of those used for mold or asbestos removal and i just ported it out the back kitchen door. I made it out of 3/4 plywood and used caulking on all the joints before i screwed it together so there weren’t any air leaks. Made it the same size filter as my old delta shop filter but it definitely out performs the delta. I did a double filter on it using a mid grade filter from the big box store and a filter i ordered online with a .1 micron rating behind it. Merv 13 i think as SSG stated. funny how all the filters sold at HD or lowes have their own rating systems so that you cant really compare them to others. none of them had any merv rating on them that i could find.
Good luck

-- In the end, when your life flashes before your eyes, will you like what you see?

View DIYaholic's profile


19623 posts in 2700 days

#6 posted 09-13-2012 03:24 AM

My air cleaner will use 3 filters. Two pre-filters (16” x 20” x 1”) on the intake, one ultra cheapo to catch really big stuff, then a MERV 9 for smallish particles. I will then have a MERV 11 (16” x 20” x 4”) on the exhaust, to filter out the itty bitty nasty microscopic stuff. My squirrel cage is wired to a variable speed control & a 12 hour timer. Grainger was supposed to call me today when my MERV 11 filter arrived. Maybe they will call tomorrow…...

-- Randy-- I may not be good...but I am slow! If good things come to those who wait.... Why is procrastination a bad thing?

View jaysonic's profile


219 posts in 2167 days

#7 posted 09-13-2012 03:49 AM

Is there a benefit to the squirrel cage type blower?

View OnlyJustME's profile


1562 posts in 2402 days

#8 posted 09-13-2012 03:54 AM

Moves more air with less noise i believe.

-- In the end, when your life flashes before your eyes, will you like what you see?

View IsaacH's profile


128 posts in 2122 days

#9 posted 09-13-2012 01:15 PM

Air filtration is a great addition to the use of “PPE” (personal protective equipment) however, f you have an actual allergy, you don’t need to rely on a “dust mask” at all. They are considered for nuisance particulate protection. An allergy warrants actual health protection. While performing any activity that creates fine dust you should be using a respirator in ADDITION to dust removal….ie sanding or sweeping. There are soft rubber respirators availabe that are inexpensive and in my opinion more comfortable than those cheap dust masks. If you’re just using the filter cartriges for dust, a respirator could actually be cheaper in the long run than the disposable masks.

(BTW, im an OSHA authorized safety trainer for the construction industry and disaster site responders)

-- Isaac- Decatur, GA - "Your woodworking....NOT machining parts for NASA!!!"

View Mainiac Matt 's profile

Mainiac Matt

8089 posts in 2353 days

#10 posted 09-13-2012 01:30 PM

Here’s your solution….

Three speed motor, timer control, remote control, very good filter….

One of the best $400 I ever invested in my shop

-- It’s the knowledge in your head, skill in your hands and motivation to create in you heart that makes you a woodworker. - Mainiac Matt

View wunderaa's profile


248 posts in 2228 days

#11 posted 09-13-2012 02:00 PM

I made my own a while back. It utilizes a double-filter stack. One 4” furnace filter, fronted by an el-cheapo filter. It works great but if I were doing it again, I’d change one thing: design it to accept the largest surface area of inlet filter possible. I currently have it tailored for 16×20” filters, but there is a quick and noticeable drop in cfm when the pre-filter is getting clogged from plowing through dirty air in the shop. If you’re a weekend warrior like me…build your own. You said you have access to A/C components, so pick the largest 110V squirrel cage motor/blower you can find and build the biggest enclosure you can stand to have. It’ll work as well or better than any commercial unit. (MY TWO CENTS!)

View Grandpa's profile


3259 posts in 2700 days

#12 posted 09-13-2012 06:41 PM

The squirrel cage blower will slip in the air and not over heat as easily as a regular fan with blades. The squirrel cage is more like a centrifigal pump as compare to a piston pump. At one time there were swamp coolers with fans then they all went to squirrel cage style blowers. There must have been a reason. More air? quieter? fewer failures on the motors? netter balance of the blades. Now if we could get those ceiling can people to change to squirrel cage designs. LOL

View AandCstyle's profile


3073 posts in 2282 days

#13 posted 09-14-2012 12:29 AM

The best solution is to catch the dust at the source before it becomes airborne. This requires a true dust collector as opposed to a shop vac. Look at Bill Pentz site for more than everything you ever wanted to know about dust collection. Be aware that a dust collection system is not cheap, but is less expensive than a trip to the emergency room.

In addition to inhaled dust being an allergen, you can also develop contact dermatitis due to the dust collecting on your skin. This would require you to keep your skin covered as much as reasonable and to shower immediately after shop time.

I would strongly suggest a great dust collector if you are into wood working for the long haul. HTH

-- Art

View jaysonic's profile


219 posts in 2167 days

#14 posted 09-14-2012 04:43 AM

Thanks IsaacH for all that info, your comment about OSHA reminded me that my father-in-law in the safety director of the school district in the area I live, he’d be good to bounce some ideas off as well.
Wunderaa, thanks for the idea about a greater surface area on the filter, as well as the link to your post. Is it beneficial to not have a cover over the air intake hole? I’ve seen a few designs where a grill cover has been placed there.
AandCstyle, I’ll definitely be investing in an actual dust collector. First though, I need to pinch some pennies for a while, with a 9mo. old, and a wife who doesn’t work and wants 3 more kids, these things are extravagances.

View wunderaa's profile


248 posts in 2228 days

#15 posted 09-14-2012 01:04 PM

Jaysonic, the hole you see is actually the air outlet. If you’re planning on having the unit mounted where someone may be able to put their hand in it, then by all means you should put a cover over it. Maybe some expanded metal of some sort…something with a low total surface area. Mine is mounted at about 8’ off of the ground and I don’t have any kids, so I opted to leave mine open. I do not, however, recommend a filter on the outlet side of the unit. Squirrel cage motor/blowers are designed to draw air in by creating a differential at the inlet, so it’s imperative that the outlet has as little restriction as possible. Hope all of this information helps and looking forward to your solution!

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