[ars]

Hot water is more efficient - heating something to 500F just to then use it to heat air to 70, or a shower to 130 is thermostatically not favorable (the bigger the difference in temperature the less energy is transferred). It's better to heat water to 180 and pump that - the initial transfer of heat from the flame is much more efficient.

Releasing the steam would be a huge waste - but of energy, not of water. The water is quite minimal.

[userbinator]

Steam is more efficient specifically because it is very hot; you don't need as much of it to transfer the same amount of energy as water, nor does steam need pumped (which also takes energy).

[jabl]

The trend in district heating systems is towards lower temperatures. Lower temperatures means that more of the waste heat in the power plant can be extracted, lower heat losses in the piping, and also if using heat pumps then lower temperatures can give a big efficiency boost. But yes, the downside is higher massflow, but this is certainly an optimization problem that engineers have calculated the optimal point for, given the available technology.

Steam heating is an ingenious invention, but it was also made in a world where pumps, the electricity to run them, PID controllers and whatnot, were expensive. That's why you tend to find it in the oldest district heating grids around.

[ars]

But it's far less efficient to create the steam in the first place. And the lack of pumping is not free, the energy comes from the steam itself.

Sure for the end users point of view it might seem more efficient but as a net hot water is far far more efficient.

[Symbiote]

No -- for one example, Copenhagen has just finished replacing the old steam-based district heating system with one based on hot water.