# secondary heat for a solar kiln



## tmbrcruiser (Feb 8, 2015)

I am interested in building a solar kiln and sawmill (Baker 3665D). The mill and shop will be heated by a wood boiler and using tubing in the concrete. The kiln will have a concrete floor. So would it work to extend the tubing into the kiln as a secondary heat source? The kiln will be 36' x 20'.


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## Tom the Sawyer (Sep 4, 2012)

tmbrcruiser,

Just to clarify you question, you intend to build a solar kiln that is 36x20' ? Or was that the size of the shop? I would think that it would take 36x20 to just contain the Baker mill. 

If that is the size of the kiln, how many board feet do you intend to dry at a time? That sounds like a 10,000 bf capacity kiln and, if you need 1 square foot of glass for each 10 bf, then you would need at least 1000 square feet of glass (or similar material). If aligned along the 36' wall you would a wall of glass 28' tall.


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## tmbrcruiser (Feb 8, 2015)

Yes, the kiln would be 36' x 20' with a capacity of just under 10,000 bf. With a 12/12 pitch this give the solar opening approximately 975 square feet and you are correct the face would be just under 28' x 36'. The shop is a separate building from the mill and kiln. The mill would adjoin the kiln. Think of a 80' x 20' mill building with a 7/12 shed type roof. The kiln would adjoin the western end of this build and have a 12/12 pitch. Loading the kiln would be from inside the mill with doors on the adjoining wall. The remaining 44' would be open for removing green lumber and a log deck for feeding the mill.


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## Post Oakie (Aug 20, 2013)

Let's back up and do a little more figuring. If you cut 3,000 board feet a day on your mill, you'll have the kiln filled in three days. Then three months to go from green to kiln dry (sounds like you're not air drying the wood first). Does that throughput meet your needs? Do you plan to incorporate a dehumidifier? With the wood back-up, you could go with less collector area, and even consider a third heat source, which would be easy if you have heat tubing in the kiln (I assume you're thinking hydronic). Also think about the temp you want in the kiln. If you want to kill bugs, it needs to get to maintain at least 135 degrees F for an hour (4/4 lumber). Other considerations: If oak weighs 5# per board ft (green) and 20% of your wood goes to slabs, 10,000 board ft will yield about 5 tons (2 cords) of slabs. So, depending on the balance between wood & solar, you may need more wood. The idea of a hybrid is good, but you need to be sure that it will meet your needs.


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## tmbrcruiser (Feb 8, 2015)

Tom the Sawyer and Post Oakie thank you for posting your questions and concerns. May be I should have supplied some understanding of my intentions for this project. So, to start I am a timber buyer for a local mill I over see procurement of approximately 12 million feet of timber and 100,000 ton of bio-mass each year. My retirement is nearing and I want a small mill operation specializing in quality woods, with some intention of saw lower grade logs as I harvest trees from my own tree farm (700 acres+/-). In this area cherry, walnut, sassafras, red & white cedar and holy are common but not plentiful. As such the mills have no interest in these logs. My intention is to mill about 5,000 ft. of these logs each month and fill in with logs from the farm sawn for the rough green market. Last week we had a job with walnut, cherry, sassafras and red cedar so I brought home about 4,600 bf. The supply of logs is not a problem for me. I am not interested in running every day but want to have something I know and enjoy to drive me. I have learned the boiler can be sized to heat the shop and kiln to a stable temperature. My hope is to use the secondary heat to make the kiln more efficient during cold weather and a night. I understand logging and timber but fall very short when it comes time to saw logs into lumber. So thank you for sharing your wisdom.


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## woodnthings (Jan 24, 2009)

*I know nothing but ....*

From what little I understand, vacuum kiln drying is THE way to go. I would at least look into it enough to see if would work for you:
http://www.amazon.com/Vacuum-Kiln-Drying-For-Woodworkers/dp/1452889260

https://images.search.yahoo.com/sea...gl-gen1&va=vacuum+kiln+drying+for+woodworkers


From some of the images it would look like a shipping container ..or 2, would make a good kiln.


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## Post Oakie (Aug 20, 2013)

Vacuum kilns are great, but at around $60,000 a bit pricy for a part-time operation, though they do produce excellent product in a short time. Tmbrcruiser from your description, I think you are on the right track! Sounds like you already know timber & marketing, so sawmilling and drying should be a piece of cake. Marketing is definitely the place where most entry-level businesses fall short!


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## tmbrcruiser (Feb 8, 2015)

Thank you guys, will keep you posted as I work through the construction phase.


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