How do I determine CFM needed to ventilate a "bedroom" workshop?

[cazclocker]

I hope this is a good spot for this question...
I didn't really build my shop... it was already an extra bedroom when we bought our home.
I took measurements, and I've found that the whole bedroom/shop has 986.7 cubic feet of volume. Lots of that volume is occupied by cabinet storage, benches, tooling and machinery, but that's how many cubic feet the bedroom is without anything in it.
I have one window to hang a fan, to blow air outside to the backyard. I haven't bought a fan yet, or even decided what kind to get.
I typically use kerosene & acetone, sometimes Coleman camp fuel. Not often, but when I do it stinks to high heaven due to zero ventilation. My wife hates it.
I guess I could just wing it and get a strong fan and see how it goes...but I wonder if any of you guys have had to install your own ventilation?
Thanks,
Doug

 

[Deleted member 69715]

I kind of doubt window fans are listed by how much air they move for a given room size. But I could be wrong.
You may have to block the HVAC's air circulation off for that room; might be helping to aggravate the wife's nose.
At any rate you might want to contact a reputable HVAC guy for an effective solution. If nothing else that would be cheaper than divorce.

 

[MrCrankyface]

A bit of a non-answer but you need a strong enough fan to make sure your room has a slight underpressure compared to the rest of the house.
I.e. some kind of exhaust ventilation that will pull air through the house, through the workshop and exhaust it outside.
This will generally keep any smells from going 'back' into the house.
How big of a fan this requires is very hard to say since a lot of factors play into it like:
-already existing ventilation system in the house
-how the wind generally hits the house
-how volatile the substances is etc.

Not sure how the climate is in kansas but exhausting all this air means more air needs to get in somewhere, and if it's cold outside this is going to cost quite a bit too.
Might be an idea to look into activated charcoal filters and recirculate/filter the rooms air or similar solutions.

 

[pontiac428]

Most work spaces need 4 air changes per hour, room under negative pressure if possible (return flow dominant). Non-recirculating air is critical for not stinking up the rest of the house, 100% of your room exhaust needs to be vented outside. Easier done than said, be creative. If you generate high hazard fumes and vapors, ramp it up to 12 air changes per hour (if you can afford the power bill). These are industrial guidelines based on mild industrial processes, YMMV, but if you were a corporation or a govermnet entity, that's the ball park for ventilation.

 

[Gaffer]

There will be others much smarter than I am to guide you, but when venting combustible vapors, I recommend an explosion-proof fan, but that may be unnecessary depending on what you are doing. You want to choose an exhaust fan that will exchange the air as much as you need. My guess is you'll want to exchange the air volume somewhere between 7-10X/hour, but that's a SWAG. Given your gross room size, I should think a 150 or so CFM fan would do just fine.

 

[Boswell]

I can't add to the CFM recommendations but will remind you that you need an inlet that is as large (or larger) than your outlet or you may not get the expected CFM. That inlet must eventually come from outside. if you section your window to allow for both inlet and outlet that might work best especially if you add some ducting to ensure that the entire room air is circulated. If the inlet comes from the rest of the house, then it will be pulled into the house from gaps around weather stripping or other openings in the house;. This will mean that in cold weather, cold outside air will come into the house and the warm air (that you paid $ to heat) will be removed via your exhaust fan. Might not be a big deal if you don't run it often or for long but something to consider. If you are able to have a slight negative pressure in the room as is suggested above and you have a central HVAC delivery vent in the room then you will be pulling a higher amount heated/cooled air from the house HVAC and so less will be available for the rest of the house. Seems nothing is simple

 

[markba633csi]

So at 100 cfm it would take about 10 minutes to change the air once. About 6 times an hour. You want at least that.

 

[Flyinfool]

Another option is to use an air to air heat exchanger so that you are not pumping all of your heated or cooled air out the window, and pulling in cold drafty air throughout the rest of the house. This way you also do not as much (you still need some) negative pressure in the room to mess with the HVAC system. There are small room sized versions. You you may need to have a drain line for condensation during the heat of summer or the cold of winter.

 

[Al 1]

IMO, Don't use those chemicals in your house. Al.

 

[Aaron_W]

When you use these stinky chemicals could you use a small paint booth?

I built one for model making that lets me use spray paint in the house to paint the models. Just a plywood enclosure open to the room with a 450 cfm squirrel cage blower that exhausts through a hole in a board wedged into a partially open window.

It works quite well, after 10 years using it I still have zero over spray outside the booth and never get complaints about odors from the family. As long as I leave it running until the paint is dry I don't smell the paint even being in the same room. I just use a common (and cheap) HVAC filter to catch the paint solids. They are not rated explosion proof but with a squirrel cage blower the motor is out of the air flow so a longer life and less chance fumes have exposure to sparks and such. Bilge blowers are another popular choice since it can be expected that a boats bilge may have some amount of fuel or oil get into the bilge water.


These are old photos from when I used it in the garage at my old place. There I just ran a length of exhaust ducting out the garage door.