Interesting, but I'm not sure that's still valid. At least for European apartments I've lived in, radiators were never sized so that they could've heated apartm

Interesting, but I'm not sure that's still valid. At least for European apartments I've lived in, radiators were never sized so that they could've heated apartments on the coldest day with wind and windows open. In older apartments cold days with wind can already be a challenge with windows permanently closed. So I guess that fell out of favor at some point when heating costs became a bigger issue.