Supplemental Heat for a Solar Kiln

Kiln owners suggest ways to "bump up" the heat at the end of a drying cycle. October 20, 2005

Does anyone have an idea on how I can bump up my kiln heat about 15 or 20 degrees? The wood is dry, but I want to see if I can bump it up a little higher to kill any bugs that may or may not be present. I thought of some sort of electric heater, but most have a thermostat that would kick off way before 130. I am using a solar kiln and will add a second layer of solar panel after I empty the kiln of its load of tiger striped red oak. It will hit around 120 now, but I don’t want to wait until July to see if it will hit 130+. I am hoping someone has crossed this bridge before and has an idea.

Forum Responses
(Sawing and Drying Forum)
From contributor A:
I had the same problem with heaters kicking out. It must be a consumer products safety commission thing. Now I just use plain old incandescent light bulbs and hang a couple of trouble lights in there like they use down at the local garage. It works great.

From Gene Wengert, forum technical advisor:
To the original questioner: You need a different type of heater; propane is often used. You also must be careful that you do not over-heat and cause a fire. Hence, use plenty of safety devices. A double layer on the clear roof will really help the heating.

Contributor A - Did you add this heat from a few light bulbs in a solar kiln? The heat losses are typically so large in a solar kiln that you need a huge amount of power.

From contributor R:
A non-thermostatically controlled kerosene jet heater and a thermostat from a hot water heater will give you lot of heat that is easy to control.

From the original questioner:
I thought about propane, but thought that might add moisture into the lumber. I may look into that but I will add the second layer for sure and see how much that will raise the temp.

From contributor A:
No, my kiln is not solar. It is a small 500 BF DH kiln with electric supplementary heat. I added the heat to get above 130F to kill PPB's at the very end of the cycle.

From contributor C:
I used emergency heat strips out of an air handler from a home AC system. You must have a fan blowing over the heat strips to keep them from glowing and burning in two. I heat my kiln to 160 degrees. The air handler will also have the appropriate safety cutout switches, thermal fuses, 24 volt transformer, contactors, etc. You can get a digital programmable thermostat for about $35. Check with industrial suppliers and refrigeration suppliers.

The fan motor is a different story. I had to run the squirrel cage fan by belt and put the motor outside the kiln away from the heat to keep it from overheating and shutting off because of the thermal protection in the motor.