I built a solar kiln last Summer. It works as expected from late Spring to early Fall. But from mid October to mid April moisture loss is on the order of 1%/month when starting with wood below 28%; might better leave it outside. So in an effort to at least extend the seasons, if not through the entire Winter, I added a false ceiling inside the kiln, and added a heater, blower, and dehumidifier, effectively turning it into a dehumidification kiln. Here's what it looked like as built:



It's 8 x 12 ft and can hold 5 - 700 bf. Fully AD 4/4 lumber will dry to 7% mc in less than 2 weeks, while nearly green 8/4 lumber takes almost 100 days in Summer. Here's what the inside now looks like with the new false ceiling:



It's just a layer of 2" closed cell foam and a layer of R19 fiberglass on top (added today). It's held by ledgers around the walls and propped up in the middle on the wood stacked below. If you look closely you will see the back of the dehumidifier, too. On the other end is the fan and heater:




The blower fits in a baffle to block off the end of the wood stack, forcing the air to the front of the kiln and back through the stack. The heater is a 1500 W oil filled heater, now set at 900 W. I loaded the kiln with 500 BF of 6/4 and 8/4 walnut at about 34% MC last week and in the first 5 days it has averaged a moisture loss of 2%/day with a temperature of 105 - 112F. This morning it was 30F and the temp. had dropped off to 101F (still a 70 deg delta which seemed amazing with only 2" of foam for a celing) so I added the R19 fiberglass on top. My calculations showed that at 20F it should take about 1200 W of heat to keep the inside of the kiln at 110F, assuming I add a layer of 2" foam to the walls and floor, which is yet to be done. If true, that should allow the kiln to operate through most of the Winter.

So far I'm pleased.

John