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heated make up air in a small shop1/14
I'm a one man woodshop working in a 1200sf shop. I have a wood stove for heat (along with a south wall full of windows) and I find it to work really well. A year ago I started doing my own finishing and I built a spray area in the upstairs loft of my shop. I have a 5000cfm explosion proof exhaust fan in the spray room (although I only shoot water borne finish) . The spray area is on the north end of the shop. When I spray I open a window on the south end of the shop to let in air to replace the 5000cfm. It gets filtered between the window and the spray area. When it's cold out I've been putting a 250,000 BTU portable "can" propane heater that I run on a bottle in front of the the window to heat the incoming air. It does a great job of keeping my spray area in the right temp range for the finishes that I'm using. Low budget, but it works. I would never want to use the heater in an enclosed space because the fumes are kind of intense. I did figure that it would be OK since it was being sucked through with the replacement air. As it turns out the smell, while not life threatening, is unpleasant.
Some projects go out unfinished since they are scheduled to be finished on site and a guy can only build so much stuff, so I'm not finishing on a daily or even weekly basis. I can't justify an $80K make up air heating system. So, here's my question. Has anyone else used a portable heater to do something like this that's say over 100K BTU that burns cleaner than the can that I'm using?
Did you ask about his last year? Sure seems familiar. An explosion proof fan in a shop heated by a wood stove seems a bit misdirected. I would not have guessed you can get insurance for a commercial wood shop heated by a wood stove. Anyway, I'd hit up all the HVAC guys and ask for a used LP furnace. They take them out all the time, when the owner wants a higher efficiency unit. Has the fire inspector ever stopped by?
Nope that was someone else. I saw that in the knowledge base while I was looking for information on portable, occasional use heaters.
I bought the explosion proof fan when I was getting set up because I couldn't be sure that I wasn't going to ever shoot solvents.
First off a AMU package for your size should only cost you 20-25K not 80K
when considering cost.!!
Bob nailed this one on the head..... You should have no problem getting someone to build/install a gas fired air make-up unit for that very small amount of air and have a Variable Frequency Drive installed on your Booth Fan Power section.... You can dial the booth power up & down to match the air Intake/Output and get just the right pressure... temperature for under 25,000...
A couple thoughts....a small furnace would probably be just fine for your sized shop, we're not talking $20K but less than $5k depending on whether you have gas/propane there already. As mentioned you may want to install a speed control to drop down the cfm's your moving. That will help keep all your air from shooting up the stack, otherwise consider a smaller fan.
Also you really only need the booth on while your spraying and maybe 5 or 10 minutes after. If your just letting it run all day your wasting a lot of energy. As a small 1-2 man shop I've never done enough spraying to require adding any kind of air makeup heating. Whatever was enough to heat the shop was enough. Now with water based you'll need to be a little more cautious about temperature, but you still should be able to get by with a normal furnace.
I was reading your original post and you are not likely to have an explosion if spraying water based material. However my concern would be the carbon monoxide that you are pumping into the shop. Do you have a carbon monoxide detector?
vfd cant be used on explosion proof fans,they can work for a while but will overheat motor and are not legal if thats a problem, a regular furnace even 100,000 btu will have a lot of trouble keeping up with exhaust, sunstream or masters make a really good kerosene heaters different from salamander heaters you might want to look into,they work better than can heaters, I installed a second fan thats only 10 inch that put on after i spray,
We purchased a used 8000 CFM, 800kBTU AMU for about $8500 IIRC. That was 12 years ago and it's still running good.
That said, if your portable heater is giving you good enough temps, I would make sure you have several CO detectors. If CO levels are ok, why reinvent the wheel?
I'm talking to Ventilation Direct now about a unit for a small shop, 32'x24'x9'. Unit for your size shop would be around $4,000 delivered. Extra cost would be duct work, electrical work and gas line work. Not bad really.