https://www.esmagazine.com/articles/83622-heating-with-steam-efficiently https://www.esmagazine.com/articles/83622-heating-with-steam... It looks like it's eff

https://www.esmagazine.com/articles/83622-heating-with-steam-efficiently https://www.esmagazine.com/articles/83622-heating-with-steam... It looks like it's efficiency has to do with the fact that it's an entirely passive heating system - it doesn't require any infrastructure except laid pipe to operate. (I went on a Google quest after reading your comment and wondered the same thing. Thought I would share...)