I have a small custom picture framing shop and I spray water base lacquer in a small room, 13x11x9 feet, so I use a 12 inch fan that delivers 1.650 CFM. It seems that this may not be powerful enough to capture all the over spray. Any suggestions?
From contributor J:
The amount of air that is required to exhaust is: (height of room) X (width of room) X 100. This is assuming you use the whole room to spray.
If you increase the airflow to suck away your overspray, you could create other finish problems that many booth owners do not anticipate until long after their finishers complain that their booth design sucks eggs, so to speak. I am talking about ridiculous drafts and vortices of air which affect layout, flowout and flash off.
Also, the air that is being sucked out has to be replaced and that introduces the prospect of getting dust, trash, debris and even lint in your flashing off finishes. As long as your code allows you, as long as your overspray is not ruining your already finished surfaces, leave well enough alone.
Build a small booth (with filter bank and buffer area behind with your 24" fan) inside this room, spray into it. Use the formula above to derive its possible height/width sizes, knowing your fan does about 7000cfm. So maybe a 7' wide by 8' tall (7' deep, 3' buffer space, plus filter bank wall and 4 feet of spray depth = 7000cfm requirement. Make everything metal.
You'll want to change the air over twice per minute to have effective overspray removal for spraying smaller things like frames and cabinet doors. Our booth is 12x20x9 = 2160 cubic feet. With 6000 cfm we effectively change the air in the booth more than twice each minute.
The questioner's booth is 1287 cubic feet and will need to move a minimum of 2600 cfm to effectively exhaust the overspray. I would recommend a 3500-4000 cfm fan for this application. Depending on where the exhaust is going, you might want to filter it well if it comes back in the shop. Also, any air intake areas to the spray room should have filters (automotive booth sticky filters), or you will notice a lot of dust coming in with the 4000 cfm of air flowing through.
You might also consider making sure your gun is set up right. We use high quality guns with good transfer efficiency and they produce only minimal overspray even when spraying 4' x 8' sheets of plywood.