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homemade booth, intake and exhaust questions

Hi Guys,

I'm making a booth in my garage and I'm trying to determine how/where to exhaust it at, and how to set up an efficient intake system as well. It's more or less a side down draft design similar to the col-met ones you see in autobodytoomart catalogs. I plan on having 20 inch high filters across both sides, and the intake to come in from the roof near the front and back . My question is, if I start a business can I even use a homemade booth in the first place? Also, should the exhaust be vented outdoors through a chimney or window of some sort? For now it's just going to be a clean room and I figured I'd pump air into it with no exhaust fan to create a bit of positive pressure so it's better than painting in an open garage.

Any thoughts or suggestions are greatly appreciated!
I'd still make a phone call to the insurance company to verify if they would cover its use. And I think as long as it is osha compliant I see no other issues with using a home made booth.
I bought a shop with a paint booth in 1987. I sold it in 1992 and built a new shop and built a shop built paint booth. (I bought a pair of heated downdrafts with a mix room between them in 2002). Anyway, the insurance company came in somewhere in the mid nineties and did an "inspection" on the homemade/shop built booth and found no issues. They were looking to make sure the exhaust fan was a "booth fan" and rated explosion proof and the lights were explosion proof. But I got around the lighting because I sealed the glass and install the standard lighting on the outside. I still have that booth, today we use it for blasting! This is not a recommendation, this is what I did. Every situation is different.
I saved these specs when building my booth. Keep in mind that the flow of air creates a "clean area" for painting and the entire vehicle needs to be in that flow area.

Paint Booth Airflow Calculations

Scenario #1 - Air moving from ceiling at back of booth to the exhaust filters at far end of booth.
Based on these assumptions:
Surface area (ft2) = 4.4m (wide) x 2.2 m (high) x 10.76 (m2/ft2) = 102.4 ft2
Air velocity = 102.4 ft2 x 100 ft/min = 10,240 ft3/min

Scenario #2: Air entering at ceiling and moving downward toward the filters immediately above the floor along the sides of the booth.
Based on these assumptions:
Surface area (ft2) = 6.6m (long) x 4.4m (wide) x 10.76 (m2/ft2) = 312.5 ft2
Air velocity = 312.5 ft2 x 50 ft/min= 15,625 ft3/min

If you want uniform air distribution throughout the booth you should size the air intake filters accordingly. If you make the filter section too small, you can expect turbulence in the booth and this will cause paint overspray to settle on the walls, ceiling, lamps, etc. In addition, turbulence lowers transfer efficiency.