One thing that hasn’t been mentioned is make-up air, i.e. air supply to replace the air you’re blowing out through the booth. If you’re drawing a negative pressure in the room, you’re reducing the efficiency of the fan’s rating, and you’re not blowing as much air as you might think, especially if you have a tight house. Cracking a window will provide make-up air. That comes from experience during a career in microbiology laboratories using biological safety cabinets from Class 1 to Class 3. HVAC systems in negative pressure labs are designed and balanced to function with and without BSCs operating, but your house doesn’t have those engineering controls.
From: main@RealSTMFC.groups.io [mailto:main@RealSTMFC.groups.io]
On Behalf Of Matt Goodman via groups.io
Nelson raises a point worth considering - how much air is moved.
I have a off the shelf Paasche booth that vents inside the basement. That was fine for short paint sessions, or slightly longer sessions wearing a respirator - neither of which is a good long term solution.
About two years ago, I started researching how much air (in cfm) I’d have to move given the distance and number of turns the exhaust would have to navigate. I found the following site very useful for those calculations:
I also described my use case and calculations from the above site in a post on the MRH forum, and got some decent help (from one guy in particular). In the research process, I also found a HVAC guy who has air booth plans that is well done (Jim Hayes, you may especially find it useful). All that is in the post here:
This whole CFM topic turned out to be more of a brain-squeezer than I expected!
Columbus, Ohio US