Controls and Venting for a Dehumidifier Kiln

Advice on controlling the conditions in a dehumidifier kiln. August 1, 2011

I am thinking of building a home DH Kiln. I have read that you need to keep the temp at a level not to over dry the wood. This kiln will be useing a house DH unit and fans, can you put a vent to lower the temp when it gets too high? The kiln will be a size to hold 500bf of lumber.

Forum Responses
(Sawing and Drying Forum)
From contributor G:
I just crack the doors open a little to cool our DH kilns.

From Gene Wengert, forum technical advisor:
Is the DH unit inside the kiln or will you duct the air externally to the unit (and then duct it back into the kiln)? If the DH is inside, you may have to have a small thermostatically controlled fan to prevent overheating of the DH unit (you might find that 110 F is the peak temperature for your unit or it might be cooler). The risk of over-drying the wood is not a temperature related factor, it is the RH in the kiln, which you can control with the DH unit itself to avoid low RHs.

From the original questioner:
Gene the DH unit will be inside and i know that you must control the temp and RH to dry the wood. I will be using a home DH unit, so what is the best way to control the RH? We have a solar kiln but would like to have a small DH kiln to dry small amounts to sell on the short time.

From contributor K:
My DH has a built in humidistat and you just set it where you want it. If yours does not I think you can get a humidistat and run your DH through it.

From Gene Wengert, forum technical advisor:
In addition to a humidistat, you can get an exhaust fan that is operated with a thermostat. Many DH kilns do not use a humidistat, but use a timer. A small bit of experience will let you know what percentage of an hour (or three hours) on will give you the correct RH and drying rate. With a home-type DH unit, you will likely be underpowered so a timer is a good idea indeed. Full power would be 1 HP per 1 MBF.