Ventilation or Purifier?

[Nathan]

You want to go with ventilation, a filter won't keep up. To size the fan you need to determine the flow you need in cfm cubic feet per minute. Measure the volume of the room and determine how many air changes per hour you need. I am sure here is an ASHRAE standard out there for air changes per hour for smoking rooms but I can't get anything to load on my ipad. Volume * air changes / 60 gets you cfm.

Then you should determine the static pressure drop of the duct you are using. There are calculators online for this. You cfm and static pressure drop in inches of water are used to size your fan.

I'd you just buy a bathroom fan based on stated cfm it is probably at 0" of pressure to make it sound the best which isn't possible in the field. If you just go off that rating you will get less flow but it is hard to determine how much.

Sound is going to be in sones or dBA at a certain number of feet away from the unit. You can find charts online that relate the sones or dBA to known reference points so you can visualize (audioize?).

If you need any help figuring flow, pressure or selecting the fan let me know assuming you aren't going to be using your garage as a commercial space and need a PE stamp in Oklahoma or something crazy like that. In that case I will still help but will require a PO.