Setting Pitch in a Dehumidifier Kiln

DH kilns may not reach the temperatures required to set pitch in wood. Be careful of CO poisoning when supplying supplemental heat. December 11, 2007

Question
When drying pine in a low temp dehumidifier kiln, 120 F is not sufficient to set pitch. What type of heat source is used to boost the temp - electric, gas? Which is most economical and available? What is the optimum temp and duration required to set pitch in long leaf pine?

Forum Responses
(Sawing and Drying Forum)
From contributor D:
Nyle low temp units are designed for the refrigeration system to operate to 120F, but with the refrigeration off and the heat on, the system can operate to 160F(72C), which is adequate for setting pitch.

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From contributor V:
I have a Nyle L200. My kiln is well insulated. With inside temps at 125*, the outside of the kiln will have frost on it when nightly temps go below 30*. It has been my experience that the built-in 4 kw heater is not large enough to reach and hold more than 125* - 130* in winter temps. Even in the summer, it is too slow to get temps of 150* or more. I use a propane heater that can be set from 10,000 to 80,000 btu's. It may sound like I am complaining about the Nyle machine, but I am really completely satisfied with it. Heating with propane is much cheaper for me than electric heat, so the system I use works well for me.

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From contributor V:
Our Nyle 200 will hold 160F with only the built-in electric heat, but we don't have a lot of days below 30 outside. The unit is in a refrigeration container, and the last pitch set I did with a temp of 35F outside took about 6 hours to raise the air from 110 to 160F (longer for the wood).

Electricity is still pretty cheap in this area, but if I had to set pitch more often and couldn't live with the time it takes the built-in heater, propane would be fairly simple and cheap to implement.

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From contributor D:
Just remember that if you use a propane heater, it uses up the oxygen pretty fast in a tight kiln. So leave a vent open. Some people will take a horizontal heater and pull air from outside, through the heater and into the kiln. Those heaters are not designed to do that and it often will never get as hot as you want. It also wastes a lot of gas. Use a propane heater that re-circulates the air in the chamber, but be sure that it has a source of fresh air for combustion. Do not go in the kiln when it is running. You could die from that.

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From contributor V:
I agree about the dangers of a gas heater in a tight kiln. I had to work inside at full temperature for 1 1/2 hours once. I started out 10 or 15 minutes in, then 5 minutes out to cool off. By the time I got done, I could barely take 5 minutes in before I would feel exhausted. I thought it was just the heat getting to me until later in the day when I was having a headache and flu-like muscle aches. That is when it dawned on me that I had co poisoning. Now if anyone has to work inside for more than a couple minutes, we turn on the vents for a few minutes before going in.