Materials update:
The spiral SUS304 pipe came today. Ordered a 1 meter section of 150mm and 200mm along with what is called a "150 T Collar". My fabricator friend called, he had already cut a hole in some 1mm thick stainless and spot welded the collar in place.
If I had the budget for regular insulated chimney, I would have bought ready made. This assembly was Y10000 or approx $100. I also got a couple of pieces of .035 stainless to make caps for the space between the tubes. The 150 fits inside the 200 with a 25mm gap. I'll start with a couple inch layer of refractory at the bottom, then fill the balance of the tube with dry perlite. Once I get to the top, another layer of castable and another stainless ring.
Don't know if this thinking is valid or not, I think that it is important for the inner chimney to heat up as hot as possible to maintain draft. The insulation should assist with that. But it will also cool quickly?
Which is better? Fill with castable refractory and it will keep the temperature high longer, but requires longer to heat up?
Or fill all with perlite, using hi-temp gasket cement to hold the stainless caps in place?
Or my first thought?
That is probably something for Sunday or later next week.
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