I'm terrible at this math stuff...according to the Ward link my 2' x 3' x 4' downdraft requires...?...I'm never sure.
That said, my kiln is only 4 1/2" softbrick thick with a 1/2" outer layer of fiber blanket sandwiched within sheet steel and a 7" softbrick flat roof and about a 12' chimney.
I have two squirrel cage blowers on with 2" Sticktite burner tips on about 12" length pipes with the appropriate propane sized orifices.
My propane tank is a 250 gallon that has 1" gas pipe running about 22' away from the valves.
It takes a lot of adjusting and monitoring to get this puppy to cone 10 which is why I decided to go with cone 6-7 clay and glazes last year.
Per Ward's formula 2' x 3' x 4' x 30,000 BTUs/cu. ft. = 720,000?
At any rate, I can do a strong cone 7 firing, fairly even in 8-10 hours.
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