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Formula to calculate how long a 20 pound propane tank will last.
A 20 pound propane tank holds about 4.72 gallons and delivers a total of 431,000 BTU's. Divide that by the BTU/HR for the number of hours running time.
The full propane tank will operate for 15.39 hours at a 28,000 BTU level.
Example: 431,000 BTU's divided by 28,000 BTU'S=15.39 hours use.