Hot Box

[Nebraska]

If proper installation  procedures, material restrictions, and backsets are maintained it should be work as an extra  heat source to sterilize wood. They have heated many spaces safely, ( we used to heat the old hunting camp with  a couple of them) They actually  sat on the floor with some feet  on the carpet never thought much about them.  They had a low oxygen shut off and  the old trailer house we had leaked plenty of air. The  combustion  by products of burning propane  properly are water vapor and CO2. The space  would have to maintain  fresh air venting to function. I don't know how/if  it would effect the drying  process via raising humidity and such in a kiln, solar or otherwise.

[YellowHammer]

The climate in a kiln is extremely corrosive.  I've had many different heat sources that I've tried and the only ones that didn't fail relatively quickly, from days to weeks, were the completely sealed systems, like halogen lights.  Otherwise, switches corroded quickly, wires rotted, not to mention relays, thermostats, fan housing, bearing, pretty much anything that could corrode, would corrode.  Also, the elevated temperatures in a kiln will cause the life of normal parts to shorten drastically.  A kiln of a hot, acid place for a machine to operateI. I would be very careful about putting any heat source that could fail catastrophically and cause your kiln to burn down.  Electric systems have external breakers, internal breakers and such. 

Thats why I am partial to the Halogen lights.  They get very hot, put out heat, they are completely sealed, even the switches and can be operated in a harsh environment.

  

[DON FRANK]

When I posed this question my thoughts were along what Nebraska had said as far as my experience with these heaters. Reasonably safe when used with some common sense.  However I had not considered considered the corrosive issues of the environment or the issue of adequate oxygen to burn. I just figured the Btu's per dollar were cheaper in the long run.
    It sounds like halogens are the way to go. However with all of the halogen lights getting replaced with LEDs  I'm afraid they will become as rare as the old corkscrew light bulbs. I guess all we'd better stock up on them while they are available.

[doc henderson]

there are also the little 20 buck heaters you can get at WM.  plug in, no flame, some forced air.  tip over switch,  I am not sure if they cut off at a high temp.  handle on top.  we have one in our pool house for the winter.

[farmfromkansas]

I bought some one dollar halogen bulb replacements at Harbor Freight a while back, they were a dollar each or 2 for 3 dollars.  Thought that was funny.  I bought the dollar ones.  Can't help it, i'm Scottish.

[caveman]

This is the first run of the hot box since John and I redid some of the insulation inside. One of us ran it a little too hot and melted some panels.  It seemed to do okay.  I turned on the lights (heat source) when I got home Wednesday afternoon.  The air temp was in the 70's.  It was getting down to the high 40's-50's at night.  Yesterday afternoon it was sitting around 148° and late last night had only dropped to 143° while it was in the high 40's outside.  Today, the inside temp was 154° and the outside air was in the 60's although up near the metal it read a little higher.  
  We still need to seal it up a little better.  When I walk out there at night, I can see a little light shining through the cracks.   
 

[Paul Q]

Has anyone tried the ceramic heat lamps as an option just asking 

[Sod saw]

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Paul Q,

What are ceramic heat lamps?   I have not heard of them unless we use different terms around here to describe them.


.

[Broncman]

They are used for reptile cages as warming or basking lamps. Theu are on Amazon. They come in several wattages. They screw into a light socket like a light bulb. You can use the old fashion ceramic socket.

I am putting the finishing touches on my kiln and heat for sterilizing is the last thing. I thought about those ceramic heat lamps, but went with a 1500 watt 6 foot baseboard heater with a clothes dryer type 155 degree shutoff switch to replace the one in the heater.

Going to install it this weekend.  My fans alone generate enough heat to get to 100 degrees. My kiln is very well insulated and sealed.

[Don P]

I'm not an electrician, reading YH's post and looking at the specs on this, would you put a 15 amp breaker on the black line outside the box? It should carry it running but if it corrodes and shorts to case it'll pop the breaker just above that normal running current.

[K-Guy]

Can't help it, i'm Scottish.

Prove it. Wear a kilt through the winter and be regimental(no underwear). smiley_jester ;D

[Sod saw]

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Don,  Your observation about breaker size and current draw are only a guess at this point.

There is not enough information given by Broncman relating to the 1500 watt baseboard heater.  That heater could be 115 volt plug in type (although I have mostly found 4 foot [1000 watt] in the real world) or it could be 230 volt hard wired type of heater that is designed to be permanently mounted to the wall.

In my kiln I use 230 volt heaters that are mounted directly to the wall and hard wired in place with conduit.

YellowHammer is correct in observing the harsh area inside an operating kiln.   I also use halogen light fixtures that plug into outlets.  All of my heat sources are controlled by thermostat.

Back to Don's math exercise and that 1500 watt heater.  Let's pretend that the heater is 230 volt unit.  1500 watts divided by 230 volts   =  about 6  1/2     amps.     We are not allowed to load a circuit more than 80 % of the breaker & wire size capability.   So the smallest breaker (fuse) would be a 9 amp double fuse (2 pole breaker). . . . awkward.

Since most folks have normal fuse boxes or breaker boxes in use, we will probably use a 15 amp 2 pole breaker and 14 gauge wire size (or larger wire size is ok).  The breaker would connect to the black conductor as well as the red conductor.  No white conductor.  The green conductor is for ground.
The breaker box and all control circuits (electronics ) will be outside of the kiln chamber in ambient fresh air.  

On the other hand (four fingers and a thumb) we need to ask how much heat is needed for what purpose .   Is 1500 watts enough to sterilize wood?   This is a topic for another day.


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[Maximus]

I'm about where y'all are at...picking the best heat source for the final bug-killing phase.

For context, I'm a hobbyist, a knucklehead, and low-volume (lumber, that is).  For you "production" mavens with customers and ledgers, none of my thoughts are remotely useful.  I'm also focused on Red Alder 2" slabs for now b/c, A) I have lots of them, and B) if I can dry them w/o horrendous splitting, then my Doug Fir slabs should also be fine.  The slabs have been air drying outside for 1.5 yrs in about 75% relative humidity, so I'm likely looking at mid-teens moisture content to start with.

So I'm making a smaller version of this dude's garage dryer from "Logs-To-Lumber-Now".(Simple DIY Wood Drying Kiln - YouTube)

[FWIW, I was focused on the Virginia Tech (VT) solar kiln for quite a while, but 4 things talked me down: 1)  I'm not doing a lot of wood, nor for a long time (just wanna remodel the house, so counters, some furniture, island...); 2)  VT dude says solar kilns are not great for bug killing; 3)  VT dude also says solar kilns are not great for thick slabs; and 4) I live in the PNW, so optimal solar kiln running conditions are less frequent.]

So assuming the garage dehumidifier version, I'm going to go with just the dehumidifier to begin with, and maybe a small fan.  The dehumidifier (which we run in the house regularly) produces a good deal of heat and air flow all on its own.    Not too fast, not too slow, that's what I'm looking for.  There's so much natural tension in Alder grain, it will be most unforgiving of impatience.

Once the dehumidifier has done its thing, I'll do the fan + heat source thing with a temp controller set at 150 degrees.  If I can hold 140-150 for 12 hours, I'll consider the slabs clean.

That's my plan!  I'll follow up with results when I get some.  Any wise, "Ohhhh, that's not going to work b/c...", I'd really love to hear it!

[Broncman]

I have a dehumdifier kiln I built from USDFA plans. It has back wall chamber that acts as an air diffuser for the stack. Fans mounted on top.

I took a long baseboard heater, bypassed the high temp cutoff. Use an inkbird controller. 

The controller has a programmable function that will hold heat cycle to a programmable temp for a programmable time.

I set it to 150 degrees for 24 hours. It has a display to show you how many hours left at temp.

I also have a 4 inch vent fan I can program for high temp or put on a timer if needed. 

So far the baseboard heat mounted by the fans has worked good.

[doc henderson]

I think 150 for 24 hours is the standard, and that is likely for 4/4. 

[K-Guy]

For hardwoods I recommend 140°F for 24 hours.

[doc henderson]

K any increase in time for thicker slabs?