<Tr> <Th> Variant </Th> <Th> Energy (J) </Th> <Th> Notes </Th> </Tr> <Tr> <Td> Thermochemical </Td> <Td> ≡ 1054.3503 </Td> <Td> Originally, the thermochemical BTU was defined as the heat required to raise the temperature of one pound of water from its freezing point to its boiling point, divided by the temperature difference (180 ° F). The similar, thermochemical calorie was defined as the heat required to raise the temperature of one gram of water from freezing to boiling divided by the temperature difference in Celsius (100 ° C). The International Standards Organization now redefines the thermochemical calorie as exactly 4.184 J. The thermochemical BTU is then defined using the conversions from grams to pounds and from Celsius to Fahrenheit . </Td> </Tr> <Tr> <Td> 59 ° F (15.0 ° C) </Td> <Td> ≈ 1054.80 </Td> <Td> Used for U.S. natural gas pricing . </Td> </Tr> <Tr> <Td> 60 ° F (15.6 ° C) </Td> <Td> ≈ 1054.68 </Td> <Td> Chiefly Canadian . </Td> </Tr>

The number of british thermal units (btu's) required to raise 17 pounds of water by 35 degrees