Hot box ?s

[Jesse]

I just built my first real hot box. Prior I had been using a ceramic heater in front of some furnace ducting but I used it mainly for curing glue ups. I didnt trust it to be left on. The one I just made is a lot better. 6 1/2' long 1 1/2' wide and 2' tall I have 3 porcelain fixtures with 150 watt bulbs on a rheostat.
 My questions are     
 How safe is it to leave it on unattended?
What temp is optimal? Right now mine says 130 deg. and that is max with the bulbs I have. I dont know if thats accurate though. I touched the metal fixture box and its hot enough to burn you. Im just a little cautious and wanted your advice. I dont want to burn the place down.
                                                     Jesse

[Jesse]

Here is a pic of the setup.

[orcbow]

Well, Jesse- remember that the spontaneous combustion temp of wood is about 800 degrees. Wood smolders at 700 degrees F. So don't worry about the temp. But I know it still feels dangerous, I have a hot box, similar to yours, with light bulbs for heat. I get worried when the temp gets up to 120. Really, what I have read is that 25 degrees above ambient is enough to dry wood. 180 degrees is more like what a lumber kiln operates at. But I have good luck running at 100 degrees. If you are drying wet wood make sure the wet air can flow out.

 Probably more houses or shops burn because of bad electrical wiring, so make sure you don't cut any corners there.

[ricktrojanowski]

I get a bit worried when I get the box going for long periods of time.  But after a while I get used to it.  I installed a dimmer switch so I can regulate the temp.  I usually run about 95-100 degrees at 40-45%RH.  If  the humidity starts getting to low, put in a damp towel or two.  Also a small fan to circulate the air helps with drying.  You can also install a in line thermostat which will shut off the bulbs.  I got mine from Bingham projects.  It kills the lights at 180 degrees.  Just a safety precaution.

[Jesse]

Thanks for the advice. Ill dim em down a bit. The wiring is tight but I skipped the ground.  I dont think you have to ground light fixtures do you?

[ricktrojanowski]

I think when I wired mine I ran a ground to the ground screw in each of the metal boxes.  Not positive I would have to take one apart to know for sure.  It was a while ago.

[Dano]

I wouldn't keep the box any hotter than it needs to be. If you monitor RH and Temp you'll be able to maintain the right moisture content in you staves. Use this calculator it helps.
http://www.woodbin.com/ref/wood/emc.htm
I'd hook up the ground wire.

[Jesse]

Thanks Dano. The porcelain fixtures I bought at home depot do not have a ground on them or a place to put one.I could ground just the box but Im not an expert in this area. I figured if a lot of new power tools work on a two wire with no ground system and you hold them in your hands I ought to get away with it since it wont be getting touched much. I dont want to rewire the whole thing so maybe Ill just plug it into a gfci outlet. I think they add more safety than grounds anyway.

[Pat B]

Jesse, I lined my box with foil backed foam board. This helps keep the wood of the box from getting too hot and also the box holds heat better. A small fan will help with wood drying as much as heat. I put a 1" hole in the bottom of one end of my box and another in the top of the other end. This will vent out moisture when drying wood and when curing glue just plug them up.     Pat

[Jesse]

Thanks Pat I was going to use the foam and I saw combustible keep away from heat written on the foil covered foam board. I suppose wood is also combustible Foam would cut the energy usage for sure. I might have a get a sheet.

[Pat B]

Don't use the blue board. The stuff I used is a tan colored foam with foil on both sides. I don't think you should use it near open flame but I have seen no ill effects on the foam board or the box in 5 or 6 years of use. My box has a thermostat and will reach 186deg(F). I built the box to build a Bingham Projects longbow.  To control heat I just unscrew bulbs or use small wattage bulbs. For drying wood the box is usually between 90 and 100 deg(F).   Pat

[Jesse]

tHANKS AGAIN PAT

[orcbow]

Jesse- Grounding is not important, because as you noted, the light bulb bases are not grounded, and GFCI is not going to change anything if there is no ground wire. Just make sure that the wire inside your box (and outside) is the proper size and is rated for the heat.

 Modern power tools are not grounded because they are "double insulated".

But if your system has metal boxes to contain switches or the reostat, its good to connect ground wires to the boxes.

[Pat B]

By putting the insulation board over the wires you can protect them from heat also.     Pat

[Jesse]

Learn something new every day. Now if I could only remember what I learn
Thanks                          Jesse