Insulated door question

[kebwi]

I am attempting to design an insulated door. The interior face and 2" thick sides will be sheet metal enclosing a cavity (2" of course). The exterior face will either be metal or hardwood, I haven't decided yet. The cavity will contain 2" of InsBlock 19. Problem is, I don't weld. The sides will consist of tabs folded over from the inner face, then wrapped along the outer face. I might wrap a strip of metal around the edge over the tabs (riveted to each tab) but there will still be cracks and tiny holes at the corners and folds. I am not comfortable with exposing the InsBlock 19 to the oven interior in this fashion.

Thus the following proposal: What if I wrap the InsBlook 19 in foil before placing it in the door? I could either use ordinary kitchen foil (or the heavy version thereof) or perhaps some sort of flashing, any extremely thin metal would do of course. I have seen extremely thin copper flashing at HD for example.

Assuming enough "wraps" were laid around the InsBlock 19, do you believe this would adequately contain any outgasing or vaporization despite a lack of a true sealed compartment?

Additionally, would wrapping the insulation board in foil defeat the purpose of the insulation by letting all the heat transmit around the edges through the foil? I figure, if that were a real problem, then the heat would already be transmitting around the edges of the exterior sheet metal anyway, so this shouldn't be a problem (not any more so than it already is at any rate), but I just don't know. Since lots of doors have an inner metal face that wraps into metal edges and then right to the exterior of the door, it seems like heat loss through the metal comprising the door isn't generally a serious problem.

What do you think?

[nissanneill]

Re: Insulated door question

Gee, you like to make hard work out of it!
For my door, (ie. the insulated removeable door rather than the 2 cast aluminium doors), I cut a 1/2" piece of plywood to size and shape to fit into the oven entrance up against the rope seal. I then got some expanded metal and cut it also to size and shape to fit the plywood but with a 2" void into which I cut and inserted 2 layers of 1" superwool blanket. I then pushed the wooden backing into the folded metal housing and nailed it to the wood through the holes. You could also run some insulating sealing rope around the front edge perimeter if you don't have a good sealing edge in the oven entrance. An hour all up and ready to go.

Neill

[kebwi]

Re: Insulated door question

So, as I understand it, your insulation is directly exposed to your cooking interior, a large wide face of it no less, not just a small seam in an unwelded box.

One thing is, I already have lots of leftover InsBlock 19 lying around from my hearth insulation. I may as well use it up instead of buying something new.

[Tscarborough]

Re: Insulated door question

I have two doors to make. The inner, insulating door will be made like this:

2 peices of AAC approx. 3" thick will be bonded in the middle, cut to the size of the inner arch with a 1" lip. I will then cut it in half vertically (at a 45 degree angle through the door so the sides lap). I will then coat the edges with thinset, thinset two AAC handles to the back, and coat the exterior of the doors with thinset.

The outer door will just be wood, and I hope to hinge it like shutters. It is just to keep out bugs and moisture.

[splatgirl]

Re: Insulated door question

I did basically what you're describing for my original door. Foil wrapped insulation board skinned in hardi-backer that was then skinned in lightweight aluminum roll flashing. I wrapped the edges and held the whole thing together with adhesive aluminum flashing tape. It worked fine for several firings, but eventually the heat got to the tape adhesive and it came unstuck and the hardi-backer started to deteriorate. At that point I brought the whole thing to a welding shop, where the hardi-backer served as the template for an insulated steel door. Cost me $200.

[texassourdough]

Re: Insulated door question

Ouch! That seems a lot for a door!
Jay

[SteveP]

Re: Insulated door question

My original door was a pice of 1/8 in steel where I had sandwiched the insulation with some expanded metal, but I wasn't comfortable with the insulation exposed to the inside of the oven. I eventually made a second door out of aluminum. I cut a piece of flat aluminum and made a pan that would hold the insulation that would fit inside the door. I bolted the two pieces together to complete the door. I get more heat transfer than I would prefer, but I can still cook for about three days after the pizza firing. I belive the entire door cost about $60.

[kebwi]

Re: Insulated door question

Hmmm, so that's a 'no' on "taping" the thing together. Good to know. I'm hoping all structural joins will be bolt/nut or rivet in my design.

[kebwi]

Re: Insulated door question

I eventually made a second door out of aluminum. I cut a piece of flat aluminum and made a pan that would hold the insulation that would fit inside the door. I bolted the two pieces together to complete the door. I get more heat transfer than I would prefer, but I can still cook for about three days after the pizza firing.

Yep, that's basically the design I was describing above, and I was curious about heat transfer. Thanks for the input.

Cheers!

[kebwi]

Re: Insulated door question

I've started building my door. The basic design is a metal box filled with foil-wrapped InsBlock 19, with a front face of oak, so the external face will be wood, not metal, although the edges will be wrapped with metal.

Question: the oak is currently unfinished, at least I think it is. Since this is the outside of the door, can I safely treat the wood in any fashion, say with a nice stain, or is that something I shouldn't expose to the oven? Other than merely staining for appearances, what sort of finish could be applied which might actually offer some protection against the elements. Everything in Washington ends up mildewy if you don't protect it somehow.

So, what kinds of finishes, if any, would be unsafe on the outside of a door, and what kinds of finishes would help protect the wood from warping, mildewing, or otherwise generally disintegrating?

Thanks.

[splatgirl]

Re: Insulated door question

FWIW, the outer face of mine gets quite hot despite it being insulated.

[kebwi]

Re: Insulated door question

Yeah, this is an experiment. The door is constructed in such a way that if the wood rots, burns, or is otherwise lost, the rest of the door is salvageable. I can unscrew the metal from the wood and either replace the wood periodically or put something else on in its place (metal).

Perhaps if you are saying it gets pretty hot, I should be concerned about staining or varnishing it. I wouldn't want that to seep into the oven and there won't be much outward draw during backing since the flue will cool down.

[splatgirl]

Re: Insulated door question

I'm not sure I would bother but maybe you'll get better mileage out of this than I am envisioning. Maybe let your first one be the test dummy and decide from that if it's worth it to stain/varnish.

[kebwi]

Re: Insulated door question

Good idea. I think I may have to rebuild the whole thing anyway. I'm building the interior out of weldable steel, and although most of it will be inside the oven most of the time, I suspect the entire thing will become 100% rust in a matter of weeks, which is shame because I'm putting way too much effort into building it. I like my design (photos when it's done), but my materials are probably going to turn out to be a failure.

[jcg31]

Re: Insulated door question

Kebwi,

The key to keeping your wood door from turning to ash is don't let any part of the wood touch brick.

http://www.fornobravo.com/forum/f2/o...html#post54043

The door above has been in use for more than a year, as you will see in the illustration it uses fiberglass tape and rope to make the seal with the oven and to prevent the wood from hitting any portion of the oven directly (including the floor). I used marine varnish for the finish and it too hasn't suffered from the heat, and this door has closed up temps 800+

Jim