Water heater heat pumps (other than the complexity) do an excellent job of maintaining 40C temperature differentials (eg Vermont or Maine) with better than 130%

Water heater heat pumps (other than the complexity) do an excellent job of maintaining 40C temperature differentials (eg Vermont or Maine) with better than 130% wall plug efficiency. I think ideal efficiency is proportional to Tcold/dT (T in Kelvin) so it could go as high as 400% if there weren’t fluid, pump, and insulation losses. The real challenge is reliability and cost of electricity. If your power goes out and you have heating oil you can still live for a week. Brewing water temperatures peak at ~100C (pressurized steam is dangerous) and even with 20C water that’s an 80K difference so you’re down to 350% ideal, which probably puts you close to breakeven with pump losses. It’s the complexity that kills it.