BTU/°F
BTU per Fahrenheit degree
Heat capacityexact by definition
The BTU per Fahrenheit degree is the customary US unit of heat capacity, equal to exactly 1899.1005347160 J/K. The factor is exact by definition, being the International Table BTU of 1055.05585262 J divided by the 5/9 kelvin Fahrenheit degree. Since water is 1 BTU/(lb·°F), a tank holding N pounds of water has a heat capacity of N BTU/°F, which is the arithmetic that makes this unit popular.
Watch out: The degree here is an interval. A 500 lb thermal mass at 500 BTU/°F stores 10 000 BTU across a 20 F° swing, regardless of what the absolute temperatures are.
| 1 BTU/°F | 1,899.1005 J/K |