Choosing a hot water heat pump

Remember how we said there were 100 brands of hot water heat pumps in Australia? 

Well, these 100 brands make about 600 different models of heat pumps.

Let’s cover some of the key differences between the various models, and go into more detail on how to choose the right model for you. 

If you’ve just joined us, we highly recommend you read our articles about different refrigerants and different brands before you go on because these are important decisions you should make before diving into specific products. 

This article is part of our series on hot water heat pumps. See all the other articles here.

What tank size do you need?

Hot water heat pumps, like other hot water systems that store water for later use, have a water tank.

A hot water heat pump usually runs for 2-3 hours a day to refill all the hot water. In other words, the hot water tank doesn’t take that long to refill, and should easily be refilled each day.

If your family spreads out its water usage, in theory, you could get away with a tiny tank. The purpose of a larger tank is to make sure that there’s plenty of hot water even if everyone takes a shower one after the other. 

Each person uses up to 50 litres of hot water a day. When choosing a tank size you want to consider the size of the house, not just who’s living there at the moment. 

What about guests?

You might have guests staying over, or your family might grow. It would really suck to buy a 4-bedroom house for your family of 6 and find out later that the hot water system is only big enough for 2 people. 

50 litres per potential occupant is a good rule of thumb, but there are other variables:

  • As you have more people in a household, you tend to use less than 50L of hot water per person on average because there’s a lower chance that everybody uses a full 50L of hot water each day or takes a shower right after each other. 
  • Heat pumps are less efficient when it’s colder. So in winter or in colder climates, they heat water a little slower. 
  • Some refrigerants are also much less effective at lower temperatures

Every hot water heat pump has a specification sheet that tells you how many people the system can cater for. 

You can combine these guidelines with what we talked about above, so if you’re deciding between two different sizes, you can make a better decision.


Noise is one of the key differences between different models of hot water heat pumps.

Some models can be as loud as 50 dB (a running dishwasher). Even if they only run for a few hours a day, you probably don’t want them near noise-sensitive areas like bedrooms, outdoor entertaining areas, or your neighbours.

On the other hand, the heat pumps made by premium brands have larger fans which turn slower, making them whisper (37 dB).

For heat pumps placed in noise-sensitive areas, we recommend getting a heat pump no louder than 43 dB. You can find the noise rating of each model in the specification sheet.

Split system vs All-in-one (Integrated)

Hot water heat pumps come in two configurations.

Split systems have the water tank and the heat pump as separate units. This means that you can have the tank in one location and have the heat pump in another (nearby location). 

This gives you more flexibility in terms of placement. For example, you could have the water tank inside, but the heat pump unit outside.

Split system hot water heat pump.

All-in-one systems (integrated systems) are a single unit. They take up less space, and some people like the look of them more.

All in one hot water heat pump.

Both configurations are totally fine, some brands offer models for both, while other brands only have one or the other. 

This usually isn’t a dealbreaker unless you have a challenging layout that you need to work around. 


There’s an industry term called Coefficient of Performance (COP). 

COP describes how much water heating energy is delivered for every unit of electrical energy the heat pump uses. The higher it is, the more efficient the heat pump, and the more energy you save. 

You’ll see many heat pump brands & products brag about their industry-leading COP. Unfortunately, there isn’t an industry-wide standard for measuring COP. It depends on things like:

  • The ambient air temperature
  • The humidity
  • Temperature of the inlet water
  • Temperature the water is heated to

For example

  • This Sanden heat pump boasts a COP of 5.96, but at an ambient temperature of 32.45 ºC ambient with 18.74 ºC cold water inlet
  • This Aquatech heat pump reports a COP of 4.25 at an ambient temperature of 19°C, while raising the water temperature by 40°C 

How do you compare these? 

It’s hard. Without identical testing conditions, comparing COP is pretty pointless. And even if the testing conditions were the same, they’re probably not the same as the conditions you have at home. 

At the end of the day, hot water heat pumps run at pretty similar efficiencies (provided the ambient temperature isn’t too cold). Other factors like refrigerant, brand, and features are more important.


You might not think of your hot water system as a battery, but it is. 

It takes a lot of energy to heat water, and there’s a lot of energy stored in a tank of hot water. You can heat your water when electricity is cheap, and use it when electricity is more expensive. It’s a battery in the sense that it can store energy for later.

If you have solar panels, you can heat your water in the middle of the day when it’s free. 

If you don’t have solar panels, you can heat your water whenever your electricity plan gives you the cheapest electricity (often in the middle of the day or middle of the night).

To make this possible, many hot water heat pumps come with a timer to let you control when the hot water heat pump should operate. 

Electric Boosters

An electric booster is just an electric heating element inside the tank which just heats water the regular way. This is how a traditional electric storage hot water heater works. 

One reason for a booster is to act as a backup in case the heat pump fails. It’s nowhere near as powerful as the heat pump for heating water, but it helps you get some hot water before you get it fixed. This is a good reason to want a booster.

Another reason for the element is if your heat pump uses a refrigerant that doesn’t do as well in lower temperatures and if it gets cold enough, the element might be needed to get your water to a hot enough temperature. This is a bad reason to want a booster – you should just get a heat pump that’s suitable for your climate. 

Overall, we think that if you get the right hot water heat pump and get it installed correctly, an electric booster is a nice-to-have. 

Next steps

Read about what government incentives and rebates are available in Australia.

Ready to get a hot water heat pump for your house? Get an instant cost, savings and rebates estimate.