Units of Heat  BTU, Calorie and Joule
The most common units of heat BTU  British Thermal Unit, Calorie and Joule.
The most common units for heat are
 BTU (Btu)  British Thermal Unit  also known as a "heat unit" in United States
 Calorie
 Joule
BTU  British Thermal Unit
The unit of heat in the imperial system  the BTU  is
 the amount of heat required to raise the temperature of one pound of water through 1^{o}F (58.5^{o}F  59.5^{o}F) at sea level (30 inches of mercury).
 1 Btu (British thermal unit) = 1055.06 J = 107.6 kpm = 2.931 10^{4} kWh = 0.252 kcal = 778.16 ft.lbf = 1.05510^{10} ergs = 252 cal = 0.293 watthours
An item using one kilowatthour of electricity generates 3412 Btu.
 one hundred thousand (10^{5}) Btu are called a therm
Calorie
A calorie is commonly defined as
 the amount of heat required to raise the temperature of one gram of water 1 ^{o}C
 the kilogram calorie, large calorie, food calorie, Calorie (capital C) or just calorie (lowercase c) is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius
 1 calorie (cal) = 1/860 international watthour (Wh)
 1 kcal = 4186.8 J = 426.9 kp m = 1.163 10^{3} kWh = 3.088 ft lb_{f} = 3.9683 Btu = 1000 cal
Be aware that alternative definitions exists  in short:
 Thermochemical calorie
 4 °C calorie
 15 °C calorie
 20 °C calorie
 Mean calorie
 International Steam Table calorie (1929)
 International Steam Table calorie (1956)
 IUNS calorie (Committee on Nomenclature of the International Union of Nutritional Sciences)
The calorie is outdated and commonly replaced by the SIunit Joule.
Joule
The unit of heat in the SIsystem the Joule is
 a unit of energy equal to the work done when a force of one newton acts through a distance of one meter
 4.184 joule of heat energy (or one calorie) is required to raise the temperature of a unit weight (1 g) of water from 0^{o}C to 1^{o}C, or from 32^{o}F to 33.8^{o}F
 1 J (Joule) = 0.1020 kpm = 2.778 10^{7} kWh = 2.389 10^{4} kcal = 0.7376 ft.lb_{f} = 1 kg.m^{2}/s^{2} = 1 watt second = 1 Nm = 9.478 10^{4} Btu
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