[Symbiote]

Copenhagen has the same system (it's actually steam that is piped around the city; gases are much easier to move than liquids). It's called district heating.

In the basement of my building there's a heat exchange, which uses the steam to heat water. This water is piped around the building.

My fairly new apartment has a meter fitted on that hot water pipe. It measures how much heat I extract from the water, and I'm charged accordingly.

In some older buildings, they have some sort of temperature logging device on each radiator. I assume this is to charge the residents according to their usage.

[olau]

Minor thing, but Copenhagen is odd with the steam. They're in the process of moving to hot water.

The trend is towards heating the water less, houses are getting better insulation, less energy is needed, and the hotter water is more expensive when heated by a heat pump and also in losses.