This question is for either Professor Wengardt or others that have expert advice regarding building a kiln enclosure to finalize moisture content to 8 percent MC and to sterilize the wood for insects. I started building this kiln using an old steel pallet rack because it is rated to handle weight and will be easy to move if needed. I have read information from the Drying Eastern Hardwood Lumber, the U.S. Forestry dry kiln build and also studied the Nyle's plans on dry kiln enclosure. I have a few questions concerning insulation, type of fans and CFM required, and what type of heat source and dehumidifier would be needed to bring down the moisture content.
First on insulation, the inside floor has 2 layers of 2" Dow XPS foamboard at R-20, 6 mil vapor barrier, 3/4 plywood. Walls are Johns Manville brand 1 1/2" Polyiso foil faced foam board which is rated at R-9.3 and the ceiling will consist of the 2 layers of the same foam board as walls but 2" and rated at R-26. Should I cover this foamboard with 6 mil visqueen before I apply the 4 mm Alucabond brand aluminum clad sheeting? Also I wanted to add more insulation to the walls on the back side to increase the R value by using either R-13 fiberglass batt which is cheap, or continue to use a thinner foam board to get the R value up past R-13? I know Professor Wengardt has mentioned about moisture getting past the surface and possibly getting into the insulation, so should I stay away from using fiberglass batt or open cell styrofoam even if I use a vapor barrier on the inside?

I plan on using this kiln to dry walnut and other more valuable wood for using in my cabinet/ woodworking business and selling the material to the public, so sterilization is the main reason for this kiln. I have in operation a solar kiln that was built in 2010 using the plans from Pro. Wengardt/Virginia Tech, and this has worked extremely well over the years in fact I am just finishing my kitchen cabinets that were built from shagbark hickory that I milled off my property.

Next on equipment, because this is such a small kiln, I wanted to use the Nyle L53 but because of "supply chain issues" they only offer the Nyle L200 which is more than I want to spend and to large for my needs, same goes for the EB LD800 that the plans that Neal Bennett designed for the U.S. Forestry. So I am looking at commercial grade dehumidifiers that are designed for crawl spaces and using monitoring systems like the Ink Bird brand that has been mentioned before on this site. The wood going into the kiln will be 8/4 walnut wood slabs 20" to 32" which is maximum width for my TimberKing 1600 to cut. Length will be 10' or under. I won't go into detail on stickers and the like because I have been reading the Drying Eastern Hardwood Lumber handbook. This walnut or other species will be air dried/solar kiln dried down to as low as I can get it for the the relative humidity in the Michigan area then finished drying to 8 percent and sterilized for bugs.

Fans, how many and how much CFM? For a 4' wide x 12' long x 7' tall chamber I want to have good circulation but not to much to overpower causing drying problems. Should I use 3 fans hanging centrally positioned off the ceiling with 12-16" diameter blades and should these fans be reversible in air movement? Also the need to cool the chamber down what size of intake and exhaust vent and should this be motorized on the exhaust side?

Heat source, I am not really planning on using this during the winter months in my pole barn because it is not heated. But during the summer months it can get warm inside the barn and this may possibly overheat the kiln. Should I be concerned with heating the inside? I have seen many plans using heat lamp bulbs, halogen work lights, or space heaters. During my high school days in wood shop I made a fiberglass re-curve bow that was placed in a plywood insulated box that was heated with an ordinary 150w incandescent light bulb and a muffin fan to circulate the air, this was back in the 70's. So this "Hot Box" should not need to much of a heat source to raise the temperature during the summer months inside the kiln. With that said, should I remove the dehumidifier once the desired MC in the wood has been achieved so that it won't overheat during the sterilization cycle.

Thanks in advance for input and advice.

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View higher quality, full size image (4032 X 1960)

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I don't see any plans for sterilizing the wood. You'll have to bring the kiln up to around 150 degrees to get the centers of the slabs up to 133 degrees to kill all stages of bugs. That's after the lumber is dry.

Just make sure your heat source meets the temps I mentioned,

Update on my Dry Kiln: It has been a slow process constructing this but I am happy to say that completion is around the corner. Busy gathering logs and cutting them on my mill have taken me away from this project and placed it on the back burner.

I finally decided to purchase the Nyle L53 kiln unit and will be taking delivery on this in a few days. I have basically followed the design plans of the Nyle kiln chambers construction plans.

Thanks for all the input on this.