Latent Heat of Vaporization (Steam)

The latent heat stored in steam and released instantly when it condenses, which is why steam is the preferred medium for delivering large quantities of heat over distance. One pound of steam delivers nearly 1,000 BTU with no temperature drop.

$$h_{fg}\approx 970\text{BTU/lb}(212^{\circ }\mathrm{F},0\text{psig})$$

Variables

Symbol	Meaning	Unit
$h_{fg}$	Latent heat of vaporization at 212°F, 0 psig	BTU/lb

Worked example

To deliver 1,000 BTU with hot water requires circulating 50 lb of water through a 20°F drop; one pound of steam delivers nearly the same energy on condensation alone.

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Part of The Blueprint of Water