Latent heat of vaporisation of water
| Value | 2,256,400 J/kg |
| Status | Conventional / typical value |
| Source | IAPWS-95; ASHRAE Handbook-Fundamentals |
| Categories | ThermodynamicMaterial Properties |
| joule per kilogram | 2,256,400 J/kg |
| foot pound-force per pound | 754,884.4 ft·lbf/lb |
| kilojoule per kilogram | 2,256.4 kJ/kg |
| joule per gram | 2,256.4 J/g |
| BTU per pound | 970.07739 BTU/lb |
| watt-hour per kilogram | 626.77778 W·h/kg |
| calorie per gram | 539.29254 cal/g |
| kilocalorie per kilogram | 539.29254 kcal/kg |
| megajoule per kilogram | 2.2564 MJ/kg |
| kilowatt-hour per kilogram | 0.62677778 kW·h/kg |
Water at any temperature
0 to 100 °CThe value above is one point on this curve. Liquid water from 0 to 100 °C at 1 atm — density, viscosity, specific heat, thermal conductivity and vapour pressure, all at the same state.
Saturated steam at any temperature
100 to 200 °CThe value above is one point on this curve. Dry saturated steam from 100 to 200 °C — saturation pressure, vapour density and latent heat along the boiling line that low and medium pressure steam heating runs on.
Learning zone
Boiling a kilogram of water at 100 °C costs 2256 kJ — 6.8 times the heat of fusion, and enough to raise the same water from freezing to boiling five and a half times over. That enormous energy density is the reason steam is used to move heat around buildings and process plants: condensing one pound of steam releases about 970 BTU at constant temperature, so a steam coil delivers heat without the flow-rate and ΔT juggling a water loop demands.
The value depends strongly on pressure and temperature. It is 2501 kJ/kg at 0 °C, 2442 at 25 °C — the figure used in psychrometrics and evaporative cooling — 2256 at 100 °C, about 2015 at 10 bar, and it falls to zero at the critical point, 373.95 °C and 22.064 MPa, where liquid and vapour become indistinguishable. Evaporative cooling towers and human sweating both trade on the 25 °C value: evaporating 1 % of a water stream cools the rest by roughly 6 K.