> 90% of the heat in that water currently goes down the drain. I think this number is very flawed, at least if we talk about bath and not shower. Kids sometime

> 90% of the heat in that water currently goes down the drain. I think this number is very flawed, at least if we talk about bath and not shower. Kids sometimes play in bath until the water is "cold". Even if they just wash, the resulting water is far cry from what it was when "inputted" into bath. Moreover, all that temp won't be recovered to heat air. Some energy goes to heat bath itself, some goes to heat space under bath and some goes to heat air. So I suspect the impact numbers to be far less benefit. And the result will be slightly warmer bath, but no effect to overall heating. But it is true that water is hungry for energy. My avg energy usage is 550kWh and I have electrical water heater. It takes exactly half of total energy usage per month.