He could probably stand to have another layer of ceramic blanket on it, but it seems to work pretty well.
Needs a sheet metal shell to contain the fibers, since you don't want to breathe those.
The main reason I like several layers of insulation is so the sheet metal jacket on exterior of the furnace remains cool to the touch over most of its area, so no accidental burns if I brush up against it.
The first time I ran my new furnace, I was shocked at how hot the 1" Mizzou hot face got.
It was very bright red on the exterior.
It is amazing how much heat Mizzou will withstand.
Mizzou will crack, which can be easily patched, but it will not crumble at iron temperatures, and stands up well to slag splatter too.
2,500 F insulating fire brick will fold like a wet waffle after one exposure to oil burner temperatures.
Don't ask me how I know this.
Anyone want to buy some powdered brick?
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