Airtight Workshop Ventilation
Hi All,
I am in the process of renovating an existing garage in Seattle, Climate Zone 4C. The foundation, floor, and walls are all poured concrete. I have recently re-built the roof, which is now sheathed, taped, and rigorously air-sealed.
My half of the garage is approximately 9’x20′; it will be insulated and used as a woodshop. I plan to use a ceiling mounted unit heater and may need a dehumidifier as well. Other than the custom carriage doors I will build on one end, there are no windows, doors, or other penetrations planned for the structure (I want to maximize workspace and wall storage).
My question is regarding fresh air and ventilation. I will likely be storing finishes, glues, and other solvents in this space, not to mention using them when finishing projects. I have seen in other similar posts a recommendation for using a 100cfm bath fan for discharging polluted air. I could monitor the air quality in the shop, crack one of the doors, and simply run as needed (or when working with finishes). Would this be sufficient for this small space? Are there other issues I should consider?
I should mention that I always wear a respirator when working with wood in enclosed spaces, and I use organic cartridges when working with solvents. I don’t want to create an unhealthy work environment, but I also don’t want to go overboard for a space that will only see intermittent use.
Thanks to those who have posted on this subject before. Any input here would be greatly appreciated.
-Adam
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Replies
How "overboard" you're going depends on how often you use the shop and in what weather. If you use it regularly in winter weather, you're going to want the doors closed to keep the heat in. Some sort of ventilation system would be a must-have. An ERV would be nice, but the sawdust is going to clog its filters (and probably the core) very fast. You can certainly use the exhaust fan and crack the windows - that's effective. Your space has +/-1800 cubic feet of volume. A 100 cfm fan will change the air every 18 minutes. That seems pretty reasonable. If you use solvent finishes regularly, you might want a 2 speed fan (or two fans) to really move the air. You can also try to set up the location of your finishing area and the fan so that the fan is drawing air across the finishes and out, rather than letting the fumes fill the space and be diluted eventually. I've set up temporary hoods for intense finishing jobs indoors. You might want to consider something similar.
Hi Peter,
Thank you for your prompt reply; this all makes sense to me. I especially like the idea of a 2-speed fan, where I could really crank up the cfm during particularly nasty operations. This might have the added benefit of allowing me to clean the shop this way as well. Crack a door, turn on the fan, and blow off my tools and machines.
A couple of follow-up questions:
1) Do you know if the interior components of a standard bath fan are well sealed? In other words, would it be a terrible idea to occasionally discharge sawdust this way?
2) Do you have thoughts on where I should look for a 2-speed fan? What kind of form-factor and through-wall penetration are we talking about?
Thanks!
-Adam
A regular bath fan is generally not sealed at all, and will use some style of open frame motor. They are not explosion proof at all, and they will clog with sawdust. I would not consider a bath fan suitable for sawdust extraction purposes.
Two speed fans are pretty common, but usually require an extra wire. Look through the selection of fans at any box store and you should be able to find some with a two speed option.
The usual way to deal with a cabinet with solvents would be to run a slight negative pressure ALL the time, to make sure any fumes are safely vented outdoors. If you have a real concern over solvent fumes, I wouldn't use any sensors, I'd just run a small exhaust fan continuously. Trying to cycle the fan based on outside factors (CO2 concentration, etc.) risks buildup of the fumes you're trying to avoid.
For sawdust, your best option is a real dust collection system. I would advise a dust collector that vents outdoors, not one of the ones with filters that stays in your shop. The filter type units tend to put a lot of very fine particulates in the air, which you really don't want to breath.
If you don't want to put in a full dust collection system and only really need some reliable ventilation when you're sanding, I would use a centrifugal blower, the industrial versions of which mount the motor external to the blower housing so you don't have a risk of the motor fouling. Grainger has many options for this type of blower. The small and midsize blowers can be ducted using dryer vent ductwork parts, and you can wire the blower to a switch near your workbench.
Bill
I've seen where people have a mini split in a garage and basically enclose it in a wooden box with furnace filters. Maybe something like a full size Panasonic ERV routed to a custom secondary filtration box would get you what you need as far as sawdust protection?
I've thought about essentially putting in a mini paint hood in my next garage. I've done some 2 part paints with Isocyanate (also wearing organic filters), it's nasty stuff. Plus, if you're not clean shaven, the masks aren't super effective. Don't want that stuff near by where I like to breathe.
A quick look at grainger shows point of use fume extractors in the ~500cfm range. These are more for welding and other things that might make more fumes than solvents though. I believe OSHA has regulations too, you could reference that for guidance on CFMs. Obviously no OSHA requirements at home, but it can be a good guideline...
A box fan with MERV-8 filters does a pretty good job of filtering out sawdust suspended in the air without any real energy penalties for added infiltration. You can also buy shop air cleaners that are built just for this (expensive, of course). I would not count on anything but an industrial exhaust fan to handle real sawdust loads. For solvent fumes, exhausting outside is always best, with collection at the point of use the best option. While I hate the heat loss, I would never recommend using any of the available ERV/HRV options to handle either the fumes or suspended dust. They would just clog up all the time. In past shops, I have relied on recirculating filtration for the suspended dust, extraction for fumes, and burning wood scraps for heat.
I don't know how practical this is, but maybe for at least the solvent/finish/glue storage area, you could make a locker with a vent to the outdoors?