Solar kiln floor insulation??? Edit… my solar kiln project

[Nebraska]

Leaning towards 3/4 inch foil faced polyiso..  Just wondering what feelings were and others choices had been.  I could go 2 inch if need be.  Building on top of 5/4 recycled deck boards.

[Southside]

Isn't that the while open pore stuff?  I would be concerned with water getting into it. 

[Nebraska]

Well I didn't think it was, I thought it kind of looked like spray foam between aluminum foil. My plan was to sandwich it under some plywood then maybe use a cheap waterproof closeout click vinyl for the floor if it will take the heat. Or maybe cheap ceramic tile on cement board. At the rate I am moving maybe it will be done by next year. 

[blackhawk]

I would go with the 2" thick foam.  That is what I used beneath the concrete for my DH kiln.

[K-Guy]

@Southside
@Nebraska
It is moisture resistant, so I would recommend a vapor barrier between it and the floor. Use 2" of the polyiso.

[scsmith42]

I used 6" of closed cell insulation in the floor, walls and doors of 3 of mine.  They get hotter in the summer than my 4th solar that has 4" poly-iso insulation.  

[Nebraska]

6 inches may (ok will)...require me to noodle on my design a bit more. I was thinking 3.5" in walls etc. 

[scsmith42]

Re wall thickness, it depends upon how cold your climate it.  In my area I'll have solar kiln temps over 100 degrees in all but 2 months or so of the year (in my 3 kilns with the 6" insulation).  In the kiln with 3.5" insulation, it's more like 8 months of the year.

[doc henderson]

Do your thing @Nebraska.  as you get thicker there is less bang for the buck.  as Gene W told me, "It is only a solar kiln".  I think he knew I was making it too hard.  I have still not built my first trying to make it harder than it has to be.  

[farmfromkansas]

I used a welded pipe frame for a base, put some straps sticking up to bolt the floor to, then used 2x6 floor frame, turned it over and put plywood under the floor frame, turned it over and bolted the floor to the pipe frame, put 2 layers of r-11 insulation in the floor frame, put plastic down over the top, then layed t&g flooring.

[Nebraska]

Well my base is two REA poles squared up, with laminated 2x10 beams on 16" centers with a layer of recycled 5/4 deck board that were too good to haul to the land fill.  It's over kill, then insulation with some sort of plywood floor. Walls haven't been decided yet. 

[Nebraska]

I just went with an inch and a half of foam insulation in the floor.  Had a nice sunset. 
Made a little progress. 


not sure what I did to underline the text above. Just happy to get the pictures posted. 

[Nebraska]

Well it was underlined in the preview.  

[Nebraska]

[Nebraska]

Made some progress again on the kiln. Knee has started to feel like piddling around with it. Yes I'm using recycled pallets. They will get stainless steel fasteners added, soaked with solubor, and treated with some good permethrin I have on the shelf before I sheet and insulate it. 
Wind chill is supposed to zero tomorrow morning so maybe not much progress on my day off. 

[beenthere]

Permethrin apparently for termites? 

https://research.fs.usda.gov/treesearch/55509#:~:text=Permethrin%20is%20a%20common%20insecticide,loss%20compared%20to%20treated%20blocks.

[YellowHammer]

Wow, that is some wide open spaces! Beautiful country, but cold looking.  

Good progress. 

[Nebraska]

Yeah it's 7 to the good side of zero right now. Lots more corn than trees. 

Just bugs in general, it will sit on a cement grain bin slab, on 6x6 creosote REA pole skid with a doubled up 2x 10 floor joists. There's lots easier wood for the termites to get. I don't want it totally packed full of Asian Beetles. 
Thanks for the link beenthere, the product I keep at the office does have a subterranean termite label. 

Nonetheless I elect to work indoors this morning.  

[Nebraska]

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Seven degrees was too cold this morning but late afternoon wasn't too bad wind laid down and it was in the 20s so I worked a little more. God gave me a beautiful scene to finish it. 

[YellowHammer]

The cool thing is as soon as you box it in and put the clear panels on, it starts to really warm up.  Like a sunroom and it will stay comfortably warm, well before it gets finishes.  With that view, I'd probably just put me a lawn chair in there, and enjoy the sunset.  

[doc henderson]

shoulda made a round one the size of that pad that turns on a turret to follow that sun till sunset!

[Nebraska]

If I remember correctly it was a 20,000 bushel grain bin on that pad. It was sold off before we bought the place. At this point my staff is balking at the idea of loading a solar kiln with that much capacity. If it wasn't so far from the house think it would be a nice place for a hot tub cabana/ sunset deck and a little bar.    

Alas mostly it's scrap metal  storage, a level spot to air dry and a place to build small projects. 

[Nebraska]

Not really picture worthy, it was a very nice day considering last week we had below zero's. I worked on the kiln, got the roof side rafters cut out of some cottonwood 2x that dried pretty straight. I had a 1/4 of a can of ready seal and coated them to waterproof them a little. They will likely get rained on before the kiln is dried in and I have too many memories of cottonwood fence boards becoming noodles in the weather from my childhood. 
I also got the air compressor over there and put a stainless steel staple in each pallet board. That should keep it sturdy enough for a while.  I had dreams of sawing today but didn't get there.  As someone else says "tomorrow's another day".   

[Nebraska]

Short side rafters got on the night before last as it got dark. Ordered some small radiator fans to mount in a built up header at the end of the collector.  I found a couple of fairly inexpensive 12 volt solar panels to install....my question is, do I need to add a battery/ charge controller between the panels and the fans or can I just get by straight wiring them to the panels ???
I was going to add a cut off switch in to the circuit but that was it. Gets dark, fans quit running wood rests. Day light comes and we go again.  Do I need anything between??

[doc henderson]

I have one direct on a solar heater I made with boy scouts.  they were a set.  I have heard of folks using no battery.  I assume these are 12 volt fans?  If you use and inverter and 110v fans it might be better to get to a certain voltage before they kick in.  the panel and fan set together work well.  If you did a battery or two, then you could invert the voltage and maybe use a separate control for a definite on and off by voltage, time or daylight.  I worry about low voltage as the sun comes up on an ac motor.  I am not a solar power expert by all means.  batteries are a consumable, so the cost keeps going up as you increase complexity.

[Nebraska]

 9 inch 12 volt dc radiator fans probably for some kids rice rocket car project. Supposedly 650 cfm.  80 watts power required. 

[Nebraska]

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Made some progress yesterday afternoon going to add some metal hangers to the rafters and some blocking, then build the header for the door opening and the fan / tarp baffle header.  

[Nebraska]

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Got most of the plywood sheeting on the kiln. I am using 19"x 8 ft manufacturing waste I need about six more sheets to finish the non collector side of the roof and the top part of the far side. Had a nice sunset too. 

[Nebraska]

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Back roof sheeted and synthetic felt on. 

[Nebraska]

If things align today I will put the twin wall polycarbonate sheets on the collector that will be the outer glazing.  I am pondering door design. 

Do I want a door that opens up with a boat winch lift or something similar??

Two doors that open to the side with +\-a removable center post? 

Or a drop down door? 
I was leaning towards the first option but 
wondering what the brain trust thinks. 

[doc henderson]

My friend and tree service guy did one on the glaze side and the whole front hinges up with a cable and it works well.  I will add, this is not how I would have done it.  he had an existing building that he adapted, so the glaze wall was all he added.  He did not insulate much, and it was way hotter in there than outside.  He kept is light with a frame and plastic glaze.  Like Gene Wengert once told me as I overthought every aspect, "it is only a solar kiln" Dr. Gene Wengert.   

[doc henderson]

I texted my buddy, Sean.  He says it is two sections, and he can lift it by hand.  It is easier with two.



It hinges at the top.  He is the one who milled up the burl for me with his wide mill.  He is also the one who make the family table from Homey locust with all the great color..

[Nebraska]

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Glazing is  on and we had a very pretty sunset. Pretty good day overall. 

[Larry]

Do I want a door that opens up with a boat winch lift or something similar??
Two doors that open to the side with +\-a removable center post?

I hinged the entire roof. To lift I had a removable center post with a hand crank on it. Easy to load with a machine or by hand.

More pics in my gallery in the kiln section if your interested.

I built this in pre-historic times at my farm in north Missouri. It went with the farm when I sold out.

[Nebraska]

I thought about that design Larry but since I was doing this on a whim with pallets the front wall was taller and I just did it. I don't know what will become of this but I am really contemplating building two more smaller kilns to use for drying thicker wider  slabs. I have a friend who is a cabinet maker and has demand for custom tables and bar/counter tops.
 One kiln a little over 12ft and one maybe 9 ft  both front load with a lift up door. I have had enough requests to know I could do some drying for dollars. Seems more flexible schedule wise. Which would be good  for me right now. 

[Nebraska]

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Got the plywood attached fully with stainless steel staples and about 2/3 of the felt. Ran out of cap nails, T50 staples and daylight. 

[Nebraska]

Just charting some progress. 
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[Nebraska]

So the next step is to finish the felt and then design and install a door. I am still leaning on an upward opening door thinking that gravity would help it seal. 

Does anyone have strong opinions on door designs?  

Side opening will eventually sag and get tougher to close , but probably more easily built.  If I built a ramp style door I'm afraid it would be much heavier do to using it as a ramp when loading and unloading the kiln. Also tougher to seal. 

[doc henderson]

Hey doc.  Bostitch and prob. other makes a stapler the feeds the plastic caps along with staples.  Handy if you had much more to do.

[Nebraska]

Yeah I have the staples and caps in the basement my carpenter friend has the gun. I just didn't take the time to run over and borrow it from Rick. They do beat the hand nail variety. Actually using an 18 gauge stapler and caps by hand w/o auto feed isn't bad unless you need the other hand for hanging on.   I was also not motivated enough to drag the cords and the air compressor over there  its far enough away from power, it  was an extra step. 

[YellowHammer]

I built conventional side opening doors, leaks are not a problem with a solar kiln, I put my vents in the doors themselves.  I just beefed up the hinges and framing and built them stout but not overly heavy and gave the threshold a little ramp to align and allow them to be pushed into place if they sagged a little.

 

[Nebraska]

Thank you, so I don't have to worry too much about perfect air tight seals. I doodled out an overhead door plan yesterday. My brain was trying to remember circle and triangle geometry concepts so that the leading edge of the bottom of the door frame would clear the front as it swung. That stuff is a lot rusty. 

[YellowHammer]

No, not with a solar kiln. I had vents over the doors and vents on the doors themselves.  Since moisture is removed from the solar kiln via air flow, during a normal drying cycle the vents are open to some degree to let the moist air out.  The only issue would be sterilization, but that takes overpowering heat in a solar kiln, so it's a whole different ball game.

Typically, once I got my vents set correctly, I almost never had to fool with them, except for a change in season.  Pretty much a set it and forget it Easy Bake oven. 

[Tom K]

Thanks for the conversation guys. I'm at a similar point in my build, so it's helpful. 

I opted for a more traditional VT design adjusted slightly for length, with the double doors on the high side.

I like seeing your progress pictures.

[Nebraska]

Well I hope my heating for sterilization idea works but I won't have pictures until I get the inside lined. Lord only knows when I will get there.  It won't be solar.....

[doc henderson]

you can triangulate with a cable in line with the pivot of the hinge and the middle outside edge of the doors but above the hinge on the outer ends of the doors.  with a turnbuckle they can be adjusted over time.

[teakwood]

Just charting some progress.
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i didn't go thru the whole post, just kinda overlooked the pics, so excuse me if i missed something, but are those two tiny fans the only ones you install?? needs way more fans, more airflow means faster drying. i have four 170W fans (normal metal house fans, 50$ each) and they make alot of wind. bought 4 extra ones when i built the kiln for replacement because they are not industial quality. after 2 years of use they still sit in the storage room and the original ones are still going strong!

[Nebraska]

Yes they are 12  volt radiator fans that are rated at 650cfm. I just figured that they would handle the heat easily and I was going to play with some solar panels so suns up they come on sun down they rest. 
@tule peak timber 

I just wasn't sure where to start. 

[Nebraska]

I roughed out the interior volume to be about 650 cubic feet so the fans at peak should turn the air over 2x per minute roughly. 

[tule peak timber]

Yes they are 12  volt radiator fans that are rated at 650cfm. I just figured that they would handle the heat easily and I was going to play with some solar panels so suns up they come on sun down they rest.
@tule peak timber

I just wasn't sure where to start.

These are the fans that have been running since last fall. So far so good.

[caveman]

On our hot box, we have side hinged doors, and they don't sag and the doors seal well.  On our solar kiln, we have two side hinged doors with a large, heavy insulated wooden panel that is put on with the tractor between the doors.  When I was dreaming this thing up, I felt the side hinged doors would sag too much and that putting the panel in would be easy.  The ground is sand, and it is challenging to get the panel to fit just right so the doors on each side of it close properly.

If we ever get around to building another, it will have side hinged doors.  We did not put any vents in our solar kiln.  It can seal up pretty tight, but we usually just leave the doors slightly open and dump moisture for a few minutes each afternoon by leaving the doors open for a minute or so.  At one time we were running dehumidifiers at night in the kiln, but we don't now.  It does a very good job drying wood.

If I recollect, we used one thickness of chicken house foam insulation under the plywood floor of the kiln and two layers in the walls.

[Tom K]

For fans I'm going to run a pair of attic exhaust fans, 1,600 cfm each. 

When I was looking into air flow I ran across a post from Dr. Wegnert with the following 

"For the cfm needed, multiply the thickness of the sticker (inches) times the length of the pile (feet) times the number of layers, divide by 12, and then times 125 feet per minute (desired velocity). Then add 50% to this number to allow for leakage"

[Nebraska]

Unfortunately that was the topic I was researching when I saw the news about Dr Wengert's passing. It kinda took the wind out of the my sails he made a huge contribution to education regarding the lumber industry and this forum. 

So I just guessed to see if it was good enough. 

[doc henderson]

easy enough to add more fans if needed.  I think the big volume is good for things like pine.

[Tom K]

Unfortunately that was the topic I was researching when I saw the news about Dr Wengert's passing. It kinda took the wind out of the my sails he made a huge contribution to education regarding the lumber industry and this forum.

So I just guessed to see if it was good enough.

I do agree that it just seem kind of odd to be in the middle of building a kiln "The Wood Doctor" was such a proponent of, and so instrumental in right now. I feel like I should tag it somehow in his honor.

I do also agree with Doc H. that those air flow numbers are more important for pine, and may be based on green pine. If I remember right I did the calculations for my kiln (13'-6" long x 7' wide sized for 1,000 bf +/-) and I came up with around 3,700 cfm. Based on drying mostly air dried hardwoods I felt comfortable with 2,000 cfm and was going to use a pair of 1,100 cfm fans. When I went to buy them all they had in stock was the 1,600 cfm fans, so that's what I got. I don't know if too much air will be an issue with air dried hardwoods, but if it is I may need to find a way to slow them down.

[YellowHammer]

The general rule is 250 fpm for hardwoods, 600 for softwoods, so 150 is conservative.  

The main thing is to keep the WB/DB bulb depression to more than 10F for any white hardwood and pine and it is a good idea in general for most hardwoods to avoid sticker stain unless the hardwood is green

Remember that the effect of airflow goes way down as the wood dries.