It just occurred to me that I actually do have a hot water heater. Two actually. I put them in under my kitchen sink - one raises the 125F domestic water to 140F (and provides near-instant hot water), and the second takes that 140F water and heats it to 185-190F at a dedicated faucet (for filling stock pots, making large quantities of tea, etc). I think I have as much copper run to push electrons as I have to deliver the water in my kitchen sink.