@ifixcoinops Hell if I know. The only way I can imagine is a well insulated cistern in the basement and a stupid amount of plumbing, which would make the exercise more stupid than almost any other way to do the job.

@ifixcoinops @mhkohne water has a pretty high specific heat. I wonder if having two water tanks, one for hot water and a larger one for cold water (since lower temp difference between room temp and freezing) would ever make sense for the home heating/cooling and refrigeration parts, where we just want to move heat around, with the tanks managing the daily cycle part.