Understanding hot water heat pump refrigerants
Lets take a wild ride through the ups and downs of hot water heat pump refrigerants to find the best hot water heater for your home and the environment.
Sam Bendat
Updated: June 17, 2025
A few readers reached out recently and requested I go deeper into heat pumps. So take a deep breath and decompress, cause you might need it.
Heat pumps use special types of refrigerants but not all are the same
A quick recap about hot water heat pumps, heat pumps are essentially reverse air conditioners for your water. They extract heat from the surrounding air and transfer it to your water tank, using much less electricity than conventional systems. The refrigerant is the unsung hero in this process, moving through a continuous cycle of:
Grabbing heat from the air (evaporation)
Intense compression, in order to raise its temperature
Transfers that heat to water through a heat exchanger
Expands and cools to start again
Depending on the type of refrigerant used, the components and cost of the unit can vary quite significantly. A CO2 heat pump will cost more than a propane unit simply because a more complex compression cycle is happening inside the unit, and more complexity is expensive! But more on those differences in a second.
The Global Warming Potential (GWP) of the refrigerant in a heat pump
Think of the GWP as a score that measures how much heat a greenhouse gas traps in the atmosphere compared to carbon dioxide if it were to be released into the atmosphere. CO2 is the baseline with a GWP of 1, which means a refrigerant with a GWP of 600 means if let out into the environment it traps 600 times more heat than the same amount of CO2 over 100 years.
The GWP score matters because refrigerants eventually leak into the atmosphere through small system leaks over time or when your system is ultimately decommissioned. A refrigerant with a high GWP can have a massive climate impact, even in small quantities. Fortunately, due to some great international and domestic legislation, there has been an ongoing shift toward low-GWP refrigerants over the last couple of years and to great success.
There are no standards for coefficient of performance (COP) numbers
What is a COP, and why are they bad boys you might be asking? Well, it's the Coefficient of Performance (COP), and it's simply a measure of efficiency for heat pumps. It tells you how many units of heat energy you get for each unit of electrical energy you put in. For example, a heat pump with a COP of 4 produces 4kW of heating for every 1kW of electricity consumed, effectively 400% more efficient than traditional electric resistance heating. But a COP can also vary dramatically depending on operating conditions.
There is currently no set regulation for how companies need to measure the COP. So, some manufacturers test their systems in balmy 30°C conditions and then claim their system is super efficient at heating, while other better-built units have a lower COP because they test their systems using more realistic testing conditions.
So, rather than focusing on marketed COP figures, a more reliable comparison is to look at the number of Small Technology Certificates (STCs) awarded by the Clean Energy Regulator. To make this easier, I am going to put together a list of all the popular hot water heat pumps in Australia. Let me know if you want more information about reliable hot water systems.
There are two main types of refrigerants being used in Australia
When it comes to refrigerants, there are generally only two options: propane or CO2. While that sounds like a weird choice, stick with me because it's actually not all that bad. Propane (R-290): The popular mass-market option
Propane (R-290): The popular mass-market option
Market share: 81% of all models Environmental impact: Tiny (GWP of just 3) Best suited for: Most Australian homes, especially in coastal/temperate areas
If you're buying a heat pump in Australia today, chances are it uses R-290. This natural refrigerant has become dominant because it's affordable and well suited to the mild climates around the eastern states. The systems tend to be more affordable, too, since they don't need to handle the extreme pressures that fancier alternatives require.
Yes, propane is flammable, but the amount in a heat pump (about 500g) is far less than what's in your BBQ gas bottle. Popular brands that use propane are Aquatech, iStore, Emerald, and many, many more. Propane is a great option for most Aussie homes unless you live in a colder climate or want to go fancy.
Carbon Dioxide (R-744): The more expensive option
Market share: 13% of models Environmental impact: Practically zero (GWP of 1) Best suited for: Alpine regions, or people who want premium
Carbon Dioxide or R-744 is the gold standard for environmental impact and is what other refrigerants are measured against. It also performs brilliantly in cold weather, making it perfect for homes in any alpine region that gets sub-zero in the winter.
The downside? CO2 systems need to handle much higher pressures, making the equipment more robust, complex, and expensive. You'll typically pay $6,000+ for these systems, compared to $3,000-$4,000 for a comparable propane model. Popular brands for Carbon Dioxide systems are Reclaim and Sanden. CO2 systems also generally run whisper-quiet.
R-513A and R-32: The nasty synthetic alternatives
The last two refrigerants make up the remaining 6% of the market but use refrigerants that are extremely harmful to the environment if they were to escape the system.
The two refrigerants to watch out for are: R-513A (4% of models)
Moderate environmental impact (GWP of 631)
Non-flammable, which matters in some specific applications
Blend of newer and older refrigerant technologies
R-32 (2% of models)
Higher environmental impact (GWP of 675)
Mildly flammable but highly efficient
Often used in multi-purpose systems that handle both water and space heating
If you are looking for a hot water heat pump in Melbourne
I got some help researching this article from my good mate Tim, who just so happens to run a hot water heat pump company called Powrhouse down here in Melbourne. Like me, Tim is keen on exploring and researching the best products and choices out there so people get the best.
If you're thinking about switching out your gas to a heat pump then let me or Tim know. He would be happy to chat and take any questions about what kind of system is best for your specific case. He knows a lot about refrigerants so feel free to have a yarn about that too.
If you’re in Melbourne and want to explore some heat pump options, I’d encourage you to email him tim@powrhouse.au or if you want me to intro you feel free to reply to this email.