To find out how many BTUs are required, calculate your surface area (length x width), multiply by 10 and round up to the corresponding number of BTUs. For instance, an area with 1,000 sq. ft. requires 12,000 BTUs.
Example: 26 ft x 38 ft = 988 sq. ft.
988 X 10 = 9,880 > rounded up = 10,000
Number of BTUs required = 12,000 (higher number)