Calculating wall openings for my new dust collector

[Aaron Rosenthal]

My new, unassembled dust collector was just dropped off. 2HP (rated), cartridge, cyclone; 1450 CFM - I feel lie doing a "Home Improvement" grunt session!
I can't bump out the garage/workshop envelope; It's a non insulated garage, and I'm going to make an internal closet to house the unit.
The air being sucked in needs to go outside somehow. I was thinking of cutting slots between the studs (16" on center) and adding a small flashing and skinny roof line - whatever the city fathers can't see on the surveillance satellite eyeball.
Can anyone please help me with the formula to figure out the area I need to cut?

[Kevin Jenness]

Why do you need to exhaust to the outside? The air you are pulling from your machines can be returned to the workspace after filtration. If you want to dispense with the filter and exhaust outside that is another story. You can just run your exhaust duct through the wall, but you will need to have an intake as well or you will be drawing air in through all the cracks and crannies in your building.

[Jim Becker]

Aaron, you should consider venting back into the shop via a non-direct path from your closet. The same area calculation is needed...at least the same area as the cyclone outlet, but preferably a little larger in area.

[Aaron Rosenthal]

Kevin, Jim, I have been diagnosed with COPD. Years of breathing auto exhaust (taxi business), wood/drywall particles from construction, and now, woodworking.
I'm trying to mitigate any further damage as much as possible.
If I vent back into the "workshop", what's the point of making a dedicated closet for the unit? My entire premise was to isolate the dust outside of the work area.

[Kevin Jenness]

Aaron, I thought the closet was for noise control. My apologies. The size of vent to the outside is somewhat arbitrary. The velocity of the exhaust stream will be the exhaust cfm divided by the vent cross section in sq ft, if that matters. You may want to baffle the vent somehow to keep the noise down outside.

Some people vent outdoors without a filter in order to increase the airflow and avoid maintaining a filter. If you have ever cleaned a clogged cartridge you know why. If your cyclone works efficiently at dust capture and your neighbors aren't too close that may work for you.

You do need to consider where the makeup air will enter the building. In Vancouver the effect on your heating system may not be a big issue. Here in VT few shops vent their dc systems outdoors due to the climate.

[Jim Becker]

Kevin, Jim, I have been diagnosed with COPD. Years of breathing auto exhaust (taxi business), wood/drywall particles from construction, and now, woodworking.
I'm trying to mitigate any further damage as much as possible.
If I vent back into the "workshop", what's the point of making a dedicated closet for the unit? My entire premise was to isolate the dust outside of the work area.

HEPA filter on the unit...and then vent back. You will not lose whatever residual heat you have that way. If you vent outside, there's no point to a filter at all and you have to make up that air, too. In your geography, that's a major thing during the colder months. A big benefit for the closet is noise control; hence, the recommendation for the indirect path back to the shop.

[Rush Paul]

Aaron, I agree with your assessment that vent outside will definitely provide the best dust outcome. If you can do so, great!

For the exhaust sizing, the key is not to end up with any restriction in total airflow, i.e., no back pressure. If you are baffling the exhaust to reduce noise on the outside, a good rule of thumb is to make the cross-section (area) of your baffle box four times the cross-section of your intake. If no baffle box, then size the exhaust at two times the cross-section of your intake.

In determining the cross-section, keep in mind that slots and holes are restrictive. If the slots are less than 1/2" wide, they don't count. Even at 2" wide, I'd discount the area by 25-50%. If you put louvers or mesh covers over the exhaust opening, treat these as restrictive also when planning your total exhaust area.

Edit: Following thought... If you can vent outside, can you simply take the exhaust from the cyclone and send it outside without bothering with filters? I don't know what your setting may be, or how efficient your cyclone may be, but some cyclones have such good separation that exhausting directly outside in a non-urban, non-suburban, setting is certainly a feasible solution.