Vijay is on track to save $860 per year with his heat pump hot water unit.
Powrhouse install an Aquatech 270L Dynamic X8 at Vijay’s place in November 2023.
A year later, I asked Vijay to send me his energy bills for 12 months before the installation and 12 months after the installation.
I crunched the numbers to analyse the changes to his energy bills.
And in March 2026, I’ve updated the numbers to account for current gas prices – and the savings are incredible.
The remarkable outcome from this case study is that Vijay only has 2 people in the home. Households with more people in the home will have even greater savings by switching to heat pump hot water.
Gas Bills Down 👇
The easiest way to analyse the change due to the heat pump hot water unit is by looking at Vijay’s summer bills.
We can safely assume that Vijay’s not going to use his gas heater in summer.
We assume that his usage due to cooking will be similar.
Vijay’s 2023 gas bills will include usage attributable to his previous gas storage hot water unit. Having ripped this out in November 2023, his 2024 summer bills now have no gas hot water usage, so we should expect to see a decrease in his gas bills. Because we are analysing summer bills, we can assume that the usage is solely due to his heat pump hot water unit.
Vijay’s gas bill cycle is from mid November to mid March, a period of around 120 days.
Vijay’s gas bills for summer 2023 totalled 7,020 megajoules (MJ). Vijay’s gas bills for summer 2024 totalled 896 MJ (this would be the amount he uses for cooking).
This equates to a difference of 6,124 MJ over 120 days (or 34% of the year).
We then need to annualise the savings, so we divide by 34%, which means Vijay’s annual savings are estimated at 18,026 MJ.
What does this mean in dollars? Well we took the average of Vijay’s gas bills over the past 12 months: 3.1c per MJ.
This equates to gas bill savings of $563.
March 2026 update: a more realistic gas price now is 4.9 c per MJ. With savings of 18,026 MJ, that’s an annualised saving of $886!! (And gas prices are only going to keep rising).
Electricity Bills Up? 👆
The decrease in gas bills is not surprising. We’ve replaced a gas appliance with an electric appliance, so of course Vijay’s gas bills were going to decrease.
Now we analyse the impact on Vijay’s electricity bills. Have they increased and if so, by how much?
Vijay’s electricity bills don’t match up perfectly with his gas bills. His electricity bills are monthly from 26 November to 25 March. We took 4 bills, a period of 121 days.
Vijay’s usage over Summer ’24 was 1,572 kWh. Vijay’s usage over Summer ’23 was 1,475 kWh, an increase of 97 kWh.
We need to annualise this with the result being an extra 293 kWh being used per year, which we attribute to the heat pump hot water unit.
We took an average electricity rate of 7 cents per kWh, which works out as $21.74 extra per year.
It’s important to note here that Vijay has solar and we set up a timer for the unit to run during the day, so most of his heat pump hot water is powered by the solar generated on his rooftop.
Double Check
We double checked Vijay’s energy bill changes by analysing his yearly rolling usage.
Vijay’s yearly gas usage decreased by 17,629 MJ, which is consistent with the estimate from only his summer gas usage (18,026MJ). At an updated gas rate of 4.9 c per MJ, this represents $863 in savings. Vijay’s yearly electricity bills a went up only 27 kWh, an increase of $2.01.
Summary
Looking at both Vijay’s energy usage confirms that Vijay is now making considerable savings of around $840 per year with his heat pump hot water unit.
Vijay has solar, so customers without solar won’t save as much, but they’ll still save a lot (see my case study).
Vijay’s considerable savings only come from a 2-person household, so households with more people will likely save more.
Both Vijay and I are thrilled with this result.
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