Wait, a question about insulation Design Styles, Chimneys and Finish Discuss Wait, a question about insulation in the Pizza Oven Design and Installation forums; Okay, I'm confused. The best insulator (short of a vacuum) is air. It's the lowest density "material"; it transmits heat ...

[kebwi]

Okay, I'm confused. The best insulator (short of a vacuum) is air. It's the lowest density "material"; it transmits heat the least efficiently.

So, why would one fill a house enclosure with loose vermiculite? I understand how vermicrete works in a dome enclosure, but in a house enclosure, why not just seal it up so the air doesn't escape easily and then leave the enclosure empty? What does the vermiculite do?

More to the point -- since I'm thinking about doors -- why isn't the best door an enclosed space without any vermiculite or insulating board filling the enclosed cavity? What does loose vermiculite or board do in the enclosed cavity of a door? It seems like an air-filled door would be the best possible design.

I will speculate briefly on what I think the answer might be, but I'm not at all sure that I'm correct. Is this the reason? If the air stirs around too much, then the hot air moves to the external surface and transmits its heat away. If that's it, then all the vermiculite or insulating board is doing is holding the air in place, but isn't really doing the insulating, its the air that's doing the work, so to speak.

...so, all that said, what about an alternative door design as follows: multiple parallel sheets of metal enclosing small spacings (I dunno, 1/4") over a thickness of 2" or so, but no vermiculite or board, just thin sheets of metal enclosing tight air spaces to keep the air from moving two far...kind of like multi-paned storm windows.

Does that make any sense?

[Tscarborough]

Air convects, so you need something to prevent air movement.

[kebwi]

So would parallel sheets of metal work, like a storm window, or is the lateral movement within a layer still still much movement to contain the heat effectively?

[Tscarborough]

It would help, but metal is an excellent conductor. metal,wood,metal would work.

[kebwi]

Point taken. Thanks for the input.

[cynon767]

The smaller and more thermally isolated the pockets of air, the better the insulation value.