How and what makes a spray booth work? This is quite simple, there are basically only three (3) things to consider;
1. AIR -- a booth needs air and a lot of it to work properly.
2. FILTERS -- a vital and critical part that is usually slighted.
3. EXHAUST -- the method of removing contaminated air is vital.
Notice that lighting is not listed and for a good reason, it is not critical to a spray booth's operation.
It IS critical to the painter and his or her performance in the booth. The amount or number of light fixtures for any given booth is basically up to the booth manufacturer and/or the booth customer.
Only the method of construction (as it applies to spray painting) of the light fixture is subject to approval.
HOW SPRAY BOOTHS WORK
All of the following will be based on the recommendations of the National Fire Protection
Association -- Bulletin 33. NFPA 33 are the best written rules and guidelines for spray booths and are what most municipalities use for their own fire codes. The only problem is that NFPA can only advise and has no means of enforcing its rules and regulations. OSHA will back up NFPA rulings but only if they (OSHA) are called in by an employee
AIR
Booths require air, a LOT of air in order to have a good air flow through the booth. NFPA-33 and
OSHA ask for a minimum of 100 feet per minute (FPM) of air flow past the operator. For most booths this equates to needing a volume source of air of from 8,000 to 10,000 cubic feet per minute (CFM). This is a lot of air and usually more than a building can provide. Booths use air as water from a raging river. Only unlike a raging river that starts from a mild stream, the booth's need for a raging river of air must COME from a raging river of air. Again since most buildings can't provide this much air DON'T rule out an air replacement unit.

If the booth doesn't get the required air it needs then the air flow inside the booth is a lot less than the required 100 FPM. The paint over spray can't be whisked away and the painter is left standing in a cloud of over spray that eventually settles to the floor. This is why booths become dusty and dirty as well as leaving a lingering smell of paint and solvent.
FILTERS
Filters are probably THE most important part of ANY paint spray booth. There is a lot to know about filtration that the average person or even the average filter distributor doesn't know. First and foremost a filter must simply be able to do two (2) things in order to be effective. One is to be able to CAPTURE and the second is to be able to HOLD the over spray. If the filter now being used cannot do these two simple tasks then they are allowing the over spray to pass on into the exhaust chamber, fan, stack and into the outside air. This is THE leading reason that neighbors know when someone is painting. This is also how cars in the parking lot get "painted".
Cheap and junk filters that don't work can end up costing a lot of money. Good and effective filters that don't fit well into their frames or track allow contaminated air to "by-pass" them through the spaces left by poor fit. Either way the filters are NOT CAPTURING and HOLDING the over spray as required. This over spray that is allowed to pass on to the inside of the exhaust chamber, fan and stack will accumulate on these surfaces. Here is where fires start in spray booths and they have a habit of starting at night or on week ends when nobody is around. They are ignited by a phenomenon called composting.
EXHAUST
A good steel exhaust chamber with steel filter holding frames and an outlet for the stack are all required by NFPA-33. Keep this in mind if a home built booth is being considered. The exhaust fan is "sized" by the air required to provide a minimum of 100 FPM air flow in the booth. This size requirement for the exhaust fan is measured in CFM. This CFM dictates the size of fan required and the amount of air needed for a "balanced" operation. If the air the exhaust fan needs is provided to the booth then the fan doesn't have to draw it from all over the shop. The booth is happy and the shop is left "quiet".

Try mounting the fan high up in the steel exhaust stack and not against the exhaust chamber. This will allow the fan to operate quieter when one is inside the booth. Plus an axial fan operates with more efficiency when there is a few feet of exhaust stack on each end.
If the stack has a dampered stackhead at its termination it will keep the cold and wind out of the booth when the fan is off. It also will keep birds out of the booth.
No matter how complicated one’s booth my appear, it can be broken down into three (3) simple requirements for good and effective operation and they are;
1. AIR
2. FILTERS
3. EXHAUST
Failure to fully address these areas of concern will almost always result in a paint spray booth that is not very efficient and probably troublesome as well. However when these three (3) simple requirements are fully met the results are truly fantastic. Yet it is still true that in industry 95% of all troublesome booths are that way due to application or MISAPPLICATION. But of those that are
NOT troublesome due to application the owners can't wait to show them off. And usually when they do, one will never hear how much it cost. Instead the owners are eager to tell everyone how valuable it is to them and their operation.
Problems may not be solved with a new booth, though the booth sales people will say that they will. As in many cases the problems lie outside of the booth, usually involving air or the lack of it.
One may wish to talk to a spray booth consultant before any hasty decisions are made. The first step is always to "find out what is wrong". It's like going to the doctor to find out what is wrong.
After some diagnosis the doctor tells us what the problem is and what the options are. Then the decision is up to us.