Venting a Workshop
nuthin2fancy
| Posted in General Questions on
I have a 420 sq ft stand-alone woodshop in Zone 5 that is constructed of 2×6 walls with 5/8″ Advantech sheeting covered with 2″ of EPS covered with LP Smartside.
Interior walls have 2″ of sprayed foam covered with the same 5/8″ Advantech sheeting. The flat 10′ ceiling is the same 5/8″ Advantech sheeting and the attic space has 10″ of blown-in insulation.
Using a 5-HP cyclone-type DC and a high-quality air cleaner to control dust.
HVAC is a mini-split for both heating and cooling and in the four years I’ve been in the unit, the four 24″ x 48″ double-pane windows have never had any visible condensation.
We’ve had 20 below (F) and stretches of 90+ degrees with elevated humidity and the interior has always been comfortable.
I’d like to be able to do finishing inside during the winter so some sort of ventilation is necessary, but the more I read about ventilation units, ERVs, and HRVs, the more confused I become.
This is a hobby shop so the volume is low; I just want to be able do some brush-on finishing (no spraying) and vent the VOCs and such during and after finishing to the point of having reasonably clean air inside without turning the place into a meat locker.
What should I be looking for? Any suggestions are greatly appreciated.
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Replies
I'm not sure you want an ERV/HRV if you are spraying lots of tiny particles into the air. A fan exhausting to the outdoors (similar to what is recommended for garages) would probably do.
One thing, have you checked your Advantech in the attic to make sure it is not accumulating moisture? Air permeable insulation in a sealed attic (assuming that's how it's constructed) can be problematic.
Thanks for your reply.
I should have mentioned I do not intend to do any spraying - just brush work.
The attic has a continuous ridge vent and the (aluminum) soffits are all vented, so I don't believe moisture will be an issue. I didn't go into this level of detail in my initial post as I didn't think it would be relevant, but now that you mention it, I should poke my head up there to check on things.
+1 for using a real exhaust fan!
HRVs are intended for exchanging limited amounts of indoor air for outdoor air, while keeping heat loss to a minimum. They are intended to keep the air quality inside up for breathing.
In your case, you want to exhaust what is basically contaminated air to the outdoors. The air from finishing work is going to have evaporated solvents in it, and probably some sawdust, all of which is likely to cause problems with an HRV. I think you'll find you'll be much better off using a common exhaust fan instead here, and making sure you have a way for sufficient makeup air to enter the structure while the fan is running (this could be as simple as a cracked open door or window). Even a bathroom fan would work, although there are probably better options out there for your application.
BTW, I would consider venting your dust collector to the outdoors too. This will remove lots of warm air from inside, requiring more heating, but it will be better for your health in terms of dust removal. As far as I know, all of the filter-type dust collectors let a lot of very fine dust through, and it's not good to be breathing that.
Bill
Thanks for your reply. Adding an exhaust fan would be simpler, to be sure, but it creates the same issue, albeit on a smaller scale, as venting the DC; where does the replacement air come from? I discussed this with the cyclone vendor and they recommended against venting to outside for this reason as well as potential noise issues.
I guess the way GBA looks at things is that its more important to have healthy indoor conditions than to minimize energy consumption. You might want to install an Awair monitor so you can track conditions and receive alerts.
You could install a power damper somewhere and interlock it with the exhaust fan so that they'd both come on together. I'm not a big fan of the dampers that just have a spring to keep them closed, I prefer the power dampers.
There are fume extractors with activated carbon filters that don't need to be vented to the outdoors, but they're usually intended for applications with a relatively small amount of contaminants to deal with (like soldering at an electronics workstation). I don't know how well they'd hold up with a larger scale application like applying stain or paint.
I agree with Steve too, and tend to prioritize health over energy savings. What's the point of saving a bit of energy if your alternative is slowly killing yourself or risking your long term health?
Bill
There are HEPA rated filters for dust collectors. If you're doing a lot of wood working and venting to the outdoors, you might as well not even have insulation or heat anymore, it's basically going to be the outdoors (1000-1500cfm of unconditioned air is a lot).
Generally the problem with dust collectors is not that they don't filter out small particles, it's that they never collect them to begin with. Most woodworking tools will create a plume of dust, the dust collector tends to pick up the bigger pieces but not the fine dust. A MERV-13 filter will take that dust out of the air, I'm not sure that venting it to the outside would get it out any faster than running it through a filter.
Note that if the plan is to put on finishes in that shed, the fine dust will get into the finish and you'll always end up with the finish looking a bit rough. You need really clean air to get a good, shiny finish. Venting to outdoors or using a good supplmental filter to get the fines out of the air is a good idea for more than just your health here.
Bill
No idea if this would help, but maybe you could run a DIY MERV filter before and during your refinishing work. I like the one that Allison Bailes wrote about on his blog: https://www.energyvanguard.com/blog/how-make-high-merv-diy-portable-air-cleaner.
Ventilation is overkill for your intended purposes - brush on finishes in a detached hobby shop. Just wear a respirator (or not) and then leave while it dries. If it's still smelly the next day open the door or windows. This is what I do when spray painting in the winter, which is way worse for air quality.
For some perspective, for spraying cars, I wait for spring, build a spray booth inside the garage with 2 box fans for exhaust and 2 furnace filters for intake, and use a full face respirator.