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[boyland]

Interesting.

Scott I have never seen anything as such but I have never really paid much attention to others on the market. 

It takes thousands of hours in development to continue to build new products which leaves little time for much else.

It is an interesting concept never considered that myself.  Though I would think whatever metal that is exposed to the heat would be at warp risk unless it is covered with a refractory material regardless of the insulation in between the outside and inside.  Such as our E4 model has access to the secondary we utilize refractory to intensify the burn line.  I think the same concept would apply to a main door if it was exposed to high heat situations.  The maximum heat from a straight wood fire is in the 1200 range though same claim up to 1400 personally never measured that hot usually in the 1100 range, either is certainly enough to soften steel with a possible warp effect on cool down.  In the gasification models we have seen around 2000 degrees with this much heat i would think it would be at risk of burn through but i never saw that occur even with several hundred hours of testing see you have to leave certain areas exposed to insert probes to measure items such as temp this you do not do in production models but it is part of the development process.

I would have to look at the reflection material properties of the materials you mentioned compared with the inside exposure temp at peak minus the heat loss to determine outside exposed material temp or you can do it by trial and error which is the industry norm.  I would guess the inside piece of steel would be exposed to temps that could lead to warp but the outside is not thus the outside frame acts a jig that prevents the warp.  I tend to prefer in those situation not exposing the interior piece of steel to that exposure and cover it with refractory and eliminate the chance from the beginning.

Now you take the downdraft units this very much becomes a non issue because the main doors are not exposed to nearly as much heat because of the design of the boiler. Heat never really reaches the door certainly not in the same way as older style units.  So I would think on these units nearly most insulation material would work just as well because the temp exposure would be much less. 

Interesting topic

[Scott7m]

It's why a lot use the pyramid shape on the part of the door that enters the firebox.

The flat plate that's on the top of the pyramid which makes up the part closest to the fire sometimes can become distorted or develop a wave in it due to heat, but the shape around it is strong and it seems to work great.   

Empyre for example don't use the pyramid shape tho, they have some type of high temp bat insulation simply laying behind a piece of 304 stainless, it to seems to work well as I've not seen it be an issue

[BigAlsc]

I was considering cutting the inner part of the door on my ncb175 off and adding insulation and then reattaching the piece of steel. Are you saying it would be better to attach refractory to the fire side of the door as a better solution to loosing so much heat from the door?

[Scott7m]

I was considering cutting the inner part of the door on my ncb175 off and adding insulation and then reattaching the piece of steel. Are you saying it would be better to attach refractory to the fire side of the door as a better solution to loosing so much heat from the door?

Your new 175 door is insulated, although I've seen them have a few issues

It doesn't appear to be insulated as well as some others

But refractory on the front of it would be a huge help