Solar kiln materials

Advice on types of materials for letting light into your solar kiln. June 24, 2001

I am working on a solar kiln and need to decide what glazing to use. The local glass company said they would use 1/4" glass panels, either 3' x 5' or 4' x 5'. Would you go with the larger panels, knowing that fewer fasteners would mean less blocking of the sun, or with the smaller panels, being more stable and less likely to break?

Forum Responses
I would advise against using glass panels if you are building your stack in the kiln rather than outside. No matter how careful you are in loading and unloading the kiln, at some point a board will slip and hit your glazing hard enough to break it. Fiberglass greenhouse glazing is a better choice.

I agree with the above 100%. The slight decrease in efficiency is not a major concern (at least with the basic design I have developed that was featured in Wood Magazine, Virginia Tech, Univ of Wisconsin and WOODWEB).

Gene Wengert, forum technical advisor

I built a solar kiln 8 years ago from plans that were in Fine Woodworking Magazine. It was designed to use salvage glass from sliding glass doors. If I remember right, the width is 40 x 76 inches and the glass is tempered. You really have to try hard to break it. I use the kiln for hobby drying of both hard and softwoods. I can dry 2 loads a year here in the NW. I paid $8 a pane when I built the kiln.

Should I use the polycarb panels? I wish I had a source for several old sliding glass doors

I built my kiln with about $25 worth of materials my door distributor was sending to the landfill. I used discontinued Anderson double-glazed sliding doors for the top and double glazed basement windows for the sides. Call your local door fabricator/wholesaler and see if he has a pallet of cull doors or a discontinued glass size he wants to unload. I have a greenhouse (glass all sides) style kiln but the double glazing really seems to keep the heat inside. I put one single glazed door on top as a test and the snow always melts off this window first in the winter. The double glazed panels still had snow for several days.

I bought extra panels for each size just in case of breakage. The tempered glass is tougher than you think. I was walking on it during assembly. So if you can find a deal on glass, breakage isn't really a problem. Most larger door manufacturers have pallets of doors from customer returns and assembly damage that go cheap. Try going to your local lumberyard and look on the box for the distributor of sliding doors in your area.

Two layers of material are encouraged. If you go to Goodwill (or similar) stores, they may have old glass doors. I suggest using corrugated fiberglass panels from the lumberyard as the outer covering--they work well and are very durable. Make sure you also use the corrugated wood strips that support these panels and minimize leaks.

Gene Wengert, forum technical advisor

Glass that is green on the edge has high iron content and may be strong, but is not as good for solar uses as glass without the green color.

Gene Wengert, forum technical advisor

I went to the big box store and they had 3 type panels: PVC, Fiberglass and polycarb. All were clear but the fiberglass was more translucent.

Also, it occurred to me that I could use one of those type panels for the inside wall sheathing. That would not only save on buying the aluminum paint but also on the labor of painting. I could double up on that to keep it airtight also.

For the inside, I think that CD-X plywood panels would be best, as they can withstand being bumped by lumber, people, etc. The walls do need to be black, so can you paint these fiberglass panels?

Gene Wengert, forum technical advisor

OK, CDX it is. Which of the 3 types of panels would be best for the clear part facing the sun?

Fiberglass will work for sure; the others--I do not know for certain.

Gene Wengert, forum technical advisor

In that case, I'll try the fiberglass and double up to insure a more airtight fit.