heat-unit

from The Century Dictionary.

• noun The unit quantity of heat; the amount of heat required to raise 1 pound of water (also 1 kilogram, or 1 gram: see calory) through 1 degree of temperature. Thus, 1 pound of coal, upon combustion, yields about 13,500 heat-units — that is, heat enough to raise 13,500 pounds of water through 1° F.