The largest component of your electricity bill is likely to be your hot water heating during the summer and in winter it normally comes second only to heating. It’s not uncommon to use 50–75 litres of water every time you have a shower and if you are lucky enough to share your house with kids that like to dawdle in the shower or take baths it’s easy to imagine money going down the drain.
New Zealand’s building code mandates new houses to have efficient room heating for houses and this is why heat pumps have become so popular over the decades but why are we not also using heat pumps to heat our hot water too? It’s easy to understand that with a heat pump for every 1KW of energy in you then receive 3–4KW of heat out, therefore it is 3–4x cheaper to run than a conventional resistive heater. Same rule applies for hot water but we are still using resistive heating as the standard.
I upgraded to a heat pump hot water heater and I think everybody should. The lifetime savings are immense and it will help reduce the load on the electricity grid or allow you to park that new Tesla in the garage and the savings on the hot water now covers the cost of charging. A heat pump hot water heater is a bit more to put in but in most cases the payback period is less than 5 years. In fact for the average family of four you could expect to save around $500 per year on electricity.
There are different units that people can purchase but I suspect the reluctance of uptake is due to the “all in one” nature of most of the systems where the heat pump module is sitting on top of the water cylinder. Meaning the entire unit and water tank has to sit in the garage or outside. I opted for a mini split system so I have a normal water tank inside my house that still has elements if I need/want to turn them on and I have a small air-to-water heat pump unit outside that is identical to some spa pool heat pumps. I went for this setup because I expect my stainless hot water cylinder could last 30–50 years and the heat pump would probably need servicing with parts at 10 years and need a full replacement at 20 years. To swap out a mini split outdoor unit it is extremely easy, in most cases if you are good with a screwdriver you don’t even need to call a plumber and in my case I won’t even need an electrician.
If you have hydronic underfloor heating it is a no-brainer to install it because you are already buying a large air-to-water heat pump so to put an extra loop in or a heat exchanger doesn’t cost all that much at the time. I think in time we will see more heat pump options around water heating come out and I could even see Elon Musk come out with a system for houses, he has hinted at something.
So if the average house spends 30% of their electricity on hot water heating, why not bring it down to 10%. Think how long we keep houses, over the lifetime of the house the savings to the occupants would be immense. So what is holding you back from going heat pump hot water on your next build?
