Shop ventilation

KevinD

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This may be so simple I'm overlooking something, but what do you all do to clear the air in your shop? My lathe/mill room is 11'X19' and when I get to cutting on either machine things can get pretty smoky in there. Typically I'll set up a fan to blow air out of the shop and another to blow in fresh air. But with this last winter being so cold that was a bit of a non-starter for getting stuff done.

I use the cutting oil with sulfur and I'm sure that doesn't help much. I have bought a bathroom vent fan but haven't installed it as it seems the vent fan in the house isn't all that effective. Just a weak negative pressure judging by the fog on the mirror after a shower. And then I don't want to install a vent fan over each machine, to blow into the bigger shop. What am I missing here?

I have hooked up a sump pump hose to my welding hood that runs outside air from a shaded pole blower over my face for welding projects. That helps a lot. Just can't figure an equivalent for the machines.

Kevin
 
For general shop ventilation, you want to change the air every 3 to 5 minutes. Commercial restrooms run in the 3 minute range.
So assuming you and an 8 ft ceiling, 11 x 19 x 8 = 1672 cu.ft. For a 3 minute air change: 1672/3 = 557 cu.ft./min or cfm. For a 5 minute air change you are looking at 334 cfm.

A typical bathroom fan is rated at about 80 cfm. You can probably get 100 cfm ones at Lowes and Home Depot as well. So you are looking at 4 to 5 bathroom fans to do the job. Placing the fans directly over the machines will help control the fumes a lot. You can duct each of them to the outside separately or do a header. If you header them, you'll need about a 10 in diameter duct for the 3 minute air change and an 8 in diameter duct for the 5 minute air change.

You can buy bigger exhaust fans through places like McMaster-Carr.

The tougher problem is heating the air to replace all that exhaust. The equation for heating energy is Q = 1.08 x CFM x (Ti - To). I'm assuming Ohio is pretty near sea level, so the 1.08 factor does not need adjusted. Ti is your room temperature in degrees F (say 70). To is the outside temperature in degrees F (say 10). You'll have to look at the local weather to decide how cold of air you need to handle. Q will be in btu/hr.

So 1.08 x 557 x (70 - 10) = 36115 btu/hr which is about 10.5 kW. And 1.08 x 334 x (70 - 10) = 21669 btu/hr which is about 6.4 kW.

By the way, part of your bathroom problem with fogged mirrors is not the fan size, but how tight the room is. If you crack the door open just a 1/2 inch, you'll notice the fog will clear much faster. We used to always cut the bottoms of the bathroom doors to leave 1" clear between door and floor so the fan could get enough make up air.

Hope that helps,
Roger
 
Roger, great write up, Thank you.
 
Could the bathroom vent fan be more efective if hooked to a flexable dryer duct tube. The end could be fastend to the backside of the saddle and evacuate at the source.

Jake Parker
 
HF sells a axial vent fan and hoses. I don't know about the quality, but I have looked at it and it looks OK on the shelf. Item #97762 It should do a pretty good job of removing the smoke.
 
Actually, catching the smoke at the source would be much better than the general exhaust approach I outlined. I'm not sure a bathroom exhaust fan would work well. One would have to jury rig a dryer hose connection with a nice transition to the fan. You can pick up small in-line fans. I found some by Suncourt (Centrax) and NuTone. links are below. I think 100 cfm would be plenty. I would guess they run less than $100 each.

The HF fan would work as well, but it is quite a bit over-sized (1590 cfm high speed, 1380 cfm low speed).

http://www.suncourt.com/Centrax.html

http://www.nutone.com/products/filter/remote-in-line-fans-bfd444a9-4e88-4e82-ba15-010b1c53a354

http://www.harborfreight.com/8-inch-portable-ventilator-97762.html

Roger
 
Those are some great ideas. Thanks for the detailed explanation racardon, of course the desired effect is to minimize heat/cooling loss while optimizing the atmosphere. Just opening the door and setting up a couple of fans can be like working outside, whether it's summer or winter.

I think the dryer vent hose of jpfabricator has some merit and with one-size-fits-all-duct tape could be easily hillbilly engineered to be placed near the offending process. Does anyone have experience with carbon filtering? I've seen those for general home application but can't imagine they would take care of the proliferation of fumes coming off a cutter. And when Ohio went smoke free a few years back I likely missed the chance of getting one of those commercial smoke eaters for cheap.

on edit, a later revelation: I remember seeing the welding fume collector in a friends welding shop some years ago. I suppose that would be the cats-ass as far as saving on the heating/cooling bill and portability. Though the cabinet was fairly large, as I recall. Maybe 4' tall and a yard deep. Kind of klunky but I imagine a smaller more shop friendly box could be figured out... another addition to the roundtoit list.
 
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A welding fume extractor would be a good way to go. The commercial ones are probably pretty pricey, though. I did a search for "diy welding fume exhaust". The following link has a pretty good idea.

http://www.millerwelds.com/resource...p?30612-Homemade-Fume-Extractor-For-About-100

I'm thinking one bathroom exhaust fan mounted close to the saddle on your lathe might do the trick.

I think activated charcoal or carbon filters would take out most of the smoke from your metal cutting. I don't think a bathroom exhaust fan is going to handle the pressure drop through filters though.

Several years ago, I picked up a blower out of a house furnace. I got mine out of the metal pile at our local dump back when you could scavenge. Anyway, I've thought about building a 16" plywood cube to put it in with a place for filters on the inlet side. Then I could hook it up to some duct work and use it to exhaust my shop. If I used activated charcoal filters, maybe I could just recirculate the air. Someday, I will put together some sketches, but don't hold your breath.
Roger
 
In cold climates air to air heat exchangers are used to hold down the heat loss of indoor/outdoor circulation. The simplest setup is a long tube inside a tube. The heated exhaust air passes out through the inner tube made of conductive material like aluminum, and cold air is drawn in through the outer tube. They're becoming common in houses in places like North Dakota or Manitoba. I don't know how the oil in the exhaust air would affect one.

Most of my air issues are with mist from spray painting. Right now I just keep it to a minimum when it's cold, so one of these is lower on my own to do list.
 
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