Using a/c heat for heating water

So much heat from my air conditioning units is blasted into the air outside (especially during the very hot summer we’ve had in Queensland). At the same time, my heat pump has been extracting heat from the air (not affected by the a/c blast) to heat water. Surely there must be a system that uses the otherwise wasted heat from a/c to heat water. And if not, why not?


It is technically possible for the reverse:

which possibly makes more sense as aircon might not be used year around, unlike hot water. There appears to be systems overseas where aircon is used to heat water, especially in tropical areas where climate is hot all year around.

I am not sure about cooling efficiency nor functionality. Cooling efficiency as it only cools when heating water…cooling in summer might be needed for longer durations. Functionality when heating of water is required, but cooling isn’t. Similar applies if aircon heats water. Maybe an option would be a heat pump supplements aircon in summer, to reduce aircon running costs.

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I think that the waste heat from the aircon would not be hot enough to heat water to a sufficient and safe temperature. 55° plus for storage in a tank.
Have you measured the temp?

It’s possible.
However there is added complexity and cost in delivering the solution. There are commercial products for heating the swimming pool with the waste heat or for improving energy efficiency of supplying hot water to large hospitals etc.

For residential use - one example. (Edit - note brochure dated 2014. Perhaps there are good reasons it has not caught on?)

Note this is just an example. Whether it is supported in Australia and whether there are competitors I’ve not researched further. It would be interesting to compare the costs (Capital/Running) with the alternatives of stand alone heat pump or roof mounted solar with or without Solar PV.

If one searches the UK etc for zero carbon or low energy homes there are clever designs that use waste heat from all sources. Bespoke design and expensive consultants to hand.

Technical support and trade services in Australia can be very limited in capability and or very expensive relative to needs. If I relied on personal experience in Oz I’d go the simpler path of stand alone systems. IE Solar PV, multiple split system air cons, Solar rooftop HWS with electric boost (Heat Pump HWS a second choice). Battery support for Solar PV optional.

Another product (Daikin Singapore)


Good point.

A few years back we replaced our gas fired hydronic boiler with a quality condensing model. An option was an integrated boiler/hot water service. It would have made sense but the hot water service was in its early life so we declined that version. Not long after we learnt a home with the combi version had a failed part and had neither heat nor hot water for 4 days in Melbourne winter while the requisite part was sourced, delivered, and installed.

The moral is to always consider support, not just buying and installing.