Electric or Propane Heat for a Small Spray Booth?

      Unvented propane heaters add moisture to the shop air. Here, pros discuss whether that is a problem, and suggest electric-heat alternatives. December 1, 2005

Question
I have a small 500 sq ft shop in Mass, and have been heating it with a propane tube heater. It seems to put moisture into the air. I'm not sure if it will effect finishing at all. I recently built a small spray booth and this will be the first winter spraying. I spray WB only.

Forum Responses
(Finishing Forum)
How does this heater increase the moisture in the air? I spray a lot of WB, also in the Northeast, and humidity is only a problem in those few weeks when it is intense, like a month or so ago when the dew point was in the 70's and it was 90 degrees. I just apply thinner coats of WB at that time, so it won't take forever to evaporate. So even when you could squeeze water out of the air, it is still possible to use WB.



Moisture in the wood shop is not a bad thing! In fact, most wood shops here in the Northeast will go to great lengths to achieve it. Moisture in the airlines is what will cause the problems. I think the key is to have good air movement. As a coatings rep, I get more service related calls in the colder months when the heaters are fired up because it is too dry in the shops. The finish will actually skim because people tend to not let the finish flash long enough before they place the piece in front of or under the heaters to speed the dry time, when in fact they will dry the surface too quickly, causing solvent trap.


From the original questioner:
I'm spraying with a Turbine HVLP system, so hopefully moisture in the lines will not be an issue. I will be sure to dry the pieces carefully to avoid the lifting problem. Here's hoping to a warm winter!


The tube type propane heaters are unvented, so the combustion gases accumulate in the workspace. Hydrogen and oxygen (among others) accumulate, combine and increase humidity. In new construction, unvented heaters are used to keep buildings warm enough for drywall mud and paint to dry. Often, the paint will need to be repaired because it will peel. Unvented heaters should only be used temporarily, and aren't fit for man or beast.


From the original questioner:
Thanks. Any fairly affordable alternative suggestions? I have a small 400 sq ft garage shop that's fully insulated.


Go to a site that sells greenhouse supplies. They have 220-240 volt electric portable heaters that really blast. It's the same exact heater sold as an electric job site heater, but cheaper from the greenhouse guys than a heater store. I have one out in the shop. I think they are 5KW output, and about a cubic ft in size. My shop is almost 1600 sq ft with 12ft ceilings. It's well insulated and two of these heaters will bring it from 30 degrees up to 65 degrees in just about an hour, then I cut one off and cut the other one back to about 50%. They have an adjustable thermostat that will heat a room up to 105 degrees before cutting off, which would be great for that WB finish.


They are made by Marley - 5600 watts on 240 volts drawing 24 amps.


Will the heat keep up with the spray booth drawing the air out?


My guess would be no. If the shop is given a chance to really warm up and the spraying is short, then maybe, but I would think a 100,000+ BTU blower or real shop HVAC system would be needed for spraying any long period of time.

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