I’m rebuilding the door on my homemade boiler. Originally it had concrete in the door as insulation. I’ve replaced that a couple times but decided to use ceramic high temp insulation batting this time. I had a buddy weld an plate over the insulation. Probably overthinking it, but does the plate need a small vent home drilled in it so when the stove comes up to temp the air trapped in the door won’t expand and cause warping?
Assuming the weld truly is air tight, yes you could need a vent to allow for expansion. A couple small drilled holes in the bottom of the door would be fine. I'm not about to sit here and do the math on how much pressure the air in the door cavity would create (would need to know size, current pressure, steel type and thickness, etc anyway), but I doubt it is enough to warp the door or blow out a weld unless the cavity is huge, but a couple small holes in the bottom won't hurt. My boiler door accumulates the most creosote on the bottom, but not enough to hold back enough pressure to explode a door. Yours may not but even if it did it would a pressure relief valve of sorts. If it were my door I would leave it as is. If you see it bulge drill a hole.
I don’t have any on my phone. It’s an amazing work of art by a local Amish welder. Seriously. It’s a beast.
If you used ceramic insulation then I'd leave it sealed...reason being is that ceramic insulation in a cavity like that will absorb and hold any moisture that it can get...causing rust issues. So if it is welded well enough to be totally sealed then it should be fine as is. I'd use rockwool next time...it will let the moisture out if it ever absorbs any...ceramic doesn't, even at high temp.
Ok I started the stove up today and the door is too hot to touch! It was warm/hot with the concrete insulation but not this hot. Anything I can do to mitigate the heat loss? The welded on plate does not appear to be bulging at all.
If you put a plate on the inside of the door with a 1" air gap that could help block some of the radiant heat.
