We got pointed by [packrat] to a 2015 presentation by [Dan Holohan] on the history and art of steam heating systems. At the advent of central heating systems for entire buildings, steam was used instead of water or air for the transport medium. These systems were installed in landmark buildings including the Empire State Building, which still use them to this day.
A major advantage of steam-based heating system is that no pump is required: the steam will naturally rise up through the piping, condenses and returns to the origin. This can be implemented as a single pipe where condensation [Only registered and activated users can see links. ]