Heat pump vs gas hot water: the real running-cost numbers

Hot water quietly accounts for up to a quarter of a home's energy use, which makes it one of the highest-impact things you can change. The trouble is that the upfront sticker price rarely tells you the running cost, and the running cost is where the decision actually sits.

An old electric resistance tank turns one unit of electricity into one unit of heat. Gas is cheaper per unit than that but you are still burning fuel and paying a daily supply charge. A heat pump moves heat from the air instead of making it, producing roughly four units of heat per unit of power.

Run that heat pump on a timer during your solar window and the running cost drops again, because most of the energy is coming from your own roof rather than the grid.

Across a year, that is the difference between a few hundred dollars and a few tens of dollars for the same hot showers. The rebate makes the upfront swap cheaper; the efficiency is what keeps paying you back.