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Recirculating Spray-Booth Air

Regulations don't allow it, because it raises concentrations of potentially dangerous chemicals. December 1, 2005

I'd like to recirculate my spray booth exhaust back in the shop to save heat this winter. I've read other posts warning against this, but if I am only spraying WB topcoats in the booth and use good quality filters, do you think it would be possible? Also, what's a good source for filters?

Forum Responses
(Finishing Forum)
From contributor J:
NFPA 33; 7.5.1 states: Air exhausted from spray areas shall not be recirculated.

Unfortunately, it doesn't matter if you are using WB or not. All codes pertaining to spray operations assume you have the ability to use flammable liquids. Also, there are VOC's in WB coatings and recirculating them could concentrate them to explosive limits.

From the original questioner:
Thanks. That does make sense. I just wasn't sure if the WB VOC's were high enough to still cause an issue.

From contributor R:
A shop the next town over has a recirculating unit, commercially made, so there is a possibility that it can be done. He seems to get along very well with it.

From contributor K:
To recirculate the air, you must have some major air scrubbers. This equipment is not cheap. Are you trying to save on heating the makeup air? It may be cheaper just heating more air than recirculating it, depending on where you are.

From the original questioner:
Yes, ideally, I'd like to conserve some makeup air heat, but a recovery system is way beyond my means. I'm still trying to find a good way to heat my small 400 sq ft garage shop. I've been using an unvented propane heater, but can't keep doing that.

From contributor G:
Never recirculate spray booth exhaust, no matter what it is. Contributor R, are you sure they are recirculating the spray booth? More likely, it is the drying room/oven. You can do a 50/50 or 80/20 recirculation with a dry room/oven.

If you are trying to cut down on heating cost, put in a freq drive on the spray booth and run it full only when needed.

From contributor R:
Pretty sure. It's a small shop like mine, 3-4 employees. Whether it's the right application of equipment I don't know. But they have a bank of filter against which they spray. The air is taken up and there's a damper at the top they can adjust to pull a certain amount and add to the new air stream. Anyway, that's my best recollection, having looked at it a year or so ago.

From Paul Snyder, forum technical advisor:
PF Online has an article on recirculating booth air at the link below. Water-base doesn't have flammable solvents, but it does have solvents that are hazardous to personnel. Recirculating will build the concentration - the article addresses the issue.