Options for heating a finishing room

      Various ways to heat a finishing room. December 12, 2000

Question
I would like to heat my finishing room (500 square feet) separate from the rest of the shop. I only need to maintain about 60 degrees with the fan on. I looked into air make-up units last year and discovered that the unit alone would cost $10,000. How can I heat this space in a more conventional manner?

I looked into infrared heaters, but don't know if they will affect the finish or if they are safe. The one I looked at had a closed combustion system.

Our finish room has 13' ceilings, a spray booth with 8' x 7' filter wall, a 24" fan, a 1 Ĺ HP motor with AC inverter, and plenty of fresh air available (3- 24" x 48" windows). We can slow down the fan with the inverter while parts are drying. We typically only run the fan fast enough to get the over-spray out during the winter. We also steal a bit of heat from the shop through two 2' x 3' filters in the door.

I am located in northern New Jersey, where it gets very cold sometimes.

Forum Responses
I had a used gas furnace for my spray room. It was outside the spray room but still in the shop. A duct ran through the wall for the hot air. It wasn't diffused very well, so it created a lot of turbulence. Would it be possible to install a furnace outside the shop? This would act as a low budget exchanger, and with the exhaust fan at a low speed, it would pressurize the room to keep dust out.



I've used radiant tube heat in my finishing room for the last 10 years with very good results. You can't place items directly underneath hot tubes before or after you spray, or you'll get bubbling. A 15' distance over the floor is the recommended height for hanging the tubes. My ceilings are the same as yours, though, so my tubes are hung slightly below the room lighting at around 11'. At this height youíll have about a 5' area beneath the tube which is off limits for items you are finishing. Outside this boundary, we usually have no problems.

Radiant systems are not cheap to purchase and install, but are quite a bit less than air makeup. Operation cost of radiant is pleasantly low, at least here in Kansas on natural gas. Radiant heat warms objects, which then in turn warm the room. It keeps our finishing materials at a good working temperature in spite of the fact that in winter we are bringing in cold outside air to supply our booth fan. It gets a little uncomfortable for the operator when the fan is on for long periods, but when the fan is turned off, the room warms up quickly.

I am in no way saying that radiant heat provides a solution as good as a heated air makeup unit. If you can afford air makeup, don't consider anything else. A properly sized and installed makeup unit provides just the right amount of air so the booth draws optimally and your operator has maximum comfort and safety.

With radiant heat youíll still need to bring in supply air to your booth, and youíll need to do it in a way that your booth will draft well. If supply air is inadequate, negative pressure is created in the building, which causes all sorts of problems. If you have any sort of common forced air or overhead heaters operating anywhere else in the building, they will not vent themselves properly. They will also be using air for combustion that is probably contaminated with whatever you're spraying. This leads to rusted out flues and heat exchangers on a constant basis.



From the original questioner:
I could afford the make-up unit--itís just setting it up and running it that will kill me. We have a 1 1/4" gas line that runs through the booth, now supplying 2 small furnaces on the roof. The line is too small and we would need a much larger one. The gas meter is about 100' away from the booth. Not to mention the unit was 700,000 btu and must cost a fortune to operate. The air makeup unit would have to go on the roof and there are structural issues of supporting such a heavy unit. Installation could cost almost as much as the unit!

The existing gas line should handle a radiant tube heater. The booth fan never has any affect on our forced air system in the shop. I am very concerned about the infrared heat because our finish room is so small. I think we would end up with pimples! I like to leave all newly finished products in the spray room with the fan on low so the shop doesn't stink. We often cram whole jobs in there. I am in trouble if I can't store work in a 5' wide area under the heater. I was thinking of mounting the heater along the back wall and angling the deflector out into the room. This may create a wider danger zone for "pimples"?



Instead of this, do the exact opposite. Another shop I know of had a similar problem with tight quarters near a spray area. They hung the tubes near the wall and angled the deflectors toward the wall somewhat. Itís working just fine for them.

You may also be able to shield your work if it is too close to the tube. For instance, we have racks for doors and other flat things. We put a rather large piece of plywood on the top space and this shields the whole rack so we can heat the danger zone.



From the original questioner:
How would you address the issue of freezing air flowing in the window at 90 miles an hour? Is there a way to preheat this air to maybe 50-60 degrees? Maybe a forced air unit that the air would be directed through as it enters? This would be in conjunction with stealing some heated air from the shop.


The way radiant heat works overcomes this issue to a large extent. With forced air heat, you are sucking all your heat out as fast as it is generated. You are getting little or no heat gain from the air as long as the fan is on. This works if you supply enough warm air to the fan so that it does not draw heat from other areas. Unfortunately, a big time air makeup unit is the only thing I know of to accomplish this. Conventional systems will not supply enough air to the fan.

I draw fresh cold air through an open doorway at one end of a 25'x50' room. We use a screen door to catch larger debris and bugs. It gets cold for the operator standing directly in the air stream. It is tolerable, though, at least here in Kansas. Our booth fan is on intermittently, probably 60% of an average workday. So even after an extended period of drawing cold air into the room until it feels cold, the room recovers its heat quickly once the fan is shut off. This is because everything in the room is relatively warm even though the air moving through it has been frigid.

The fine assistance I received from my area's rep for Combustion Research was crucial to my being satisfied. There are many variations on these systems, and some systems (like mine) need to be configured specifically for your installation.



I have a 10' X 12' finish room built separately from my shop. For heat I use a low temp radiator. Though of modest BTU output, it has good thermal mass. This reheats the room quickly after I shut down the vent fans after a spray.

I plan to increase my output. A larger finishing facility is in the works. I'm thinking about in-floor or in-wall radiant heat. With enough area and a modest temperature the heat would be omni-directional, lack hot spots, and be most comfortable. The cold air moving through should still have minimal effect on drying, if it is intermittent. The room would be reheated by the large thermal mass of the warm walls and floor.

This system doesn't use big gulps of energy in short periods of time, but moderate energy consumption over extended periods. Your gas supply may be adequate. Additionally, there would be very little hardware taking up space in the finishing room, the boiler being outside and the radiant tubing behind wallboard or under floor.



Why don't you look into a boiler that would provide radiant heat through the use of radiators, baseboard units or fan driven convectors? I have radiant floor heat (plastic heating tubes buried in the concrete) and it works great. It keeps the room warm even with the exhaust fans on and is very energy efficient. You can install this system in the ceiling, floor, walls, anywhere you can get tubing.

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