[kqr]

And if the heat goes into water, it needs even more power because water is notoriously hard to heat up.

At one point I owned many appliances that leaked heat, and I think I learned to estimate how much power they drew simply by putting my hand on them and feeling how hot they were. I'm not sure I have that superpower anymore. (Obviously it was never that exact, because it depends on many other things like volume, material, isolation, etc. But you can get fairly close for common household things – between a finger and a few heads in size, surrounded by air, plastic case.)

[ballenf]

Or to put it another way -- if hot water goes down the drain (shower, clothes or dish washing, etc.), then that's another place the waste energy is going.

[firebird84]

Better down the drain then to radiate it back into your air. Then you gotta spend more energy pumping that heat outside (if you live in a hotter climate like I do).

[jhenkens]

Alternatively, use it to warm up the cold water coming into the shower (I'd guess the largest usage of hot water in a home). Warmer "cold" water mixing with the hot water means less hot water used out of the hot water heater. My understanding, placing this only on the cold supply to the shower is it'll only impact your showers. https://ecodrain.com/en/