How long will a propane tank last?

15,000 BTU units (1 lb propane tank)
High-flame setting: 1.4 hours
Low-flame setting: 2.3 hours

20,000 BTU units (1 lb propane tank)
High-flame setting: 1 hour
Low-flame setting: 1.7 hours

50,000 BTU units (20 lb propane tank)
High-flame setting: 8.6 hours
Low-flame setting: 13.5 hours

70,000 BTU units (20 lb propane tank)
High-flame setting: 6.2 hours
Low-flame setting: 9.6 hours