I've built a pressure canner that I'm using as a process reactor. I have had it pressure tested to 20 psig and have a pressure relief valve set at 30 psig. I need help in figuring out the following questions: How do I figure out the btu's required to bring the thermal mass of the steel canner at 60 F up to 300 F? ~ Elevation is 300' above sea level. ~ Propane is fuel source. ~ The canner is broken into three steel pieces, but welded together: 1. Bottom plate is 36" in diameter and 1/2" thick. 2. Vertical pipe (wall) is 3/8" thick and has a outside diameter of 36" and is 36" tall. 3. Top plate is 40" in diameter and is 3/4" thick. How do I figure out the btu's required to fill the canner with steam at 20 psig? How much water is needed? ~The internal volume is 36643.536 cubic inches The answers will help determine how much propane I will need to use. I do understand that once the first process has been done, the steel will hold onto 200+ degrees F of heat and the second process will take less fuel to heat to 20 psig. But if I assume the 60 F to 300 F was each process, I can assume a tank will last me so long (when actually it will last longer).