What’s the Best Type of Heat Pump Refrigerant?

At the heart of every heat pump is refrigerant. This is the gas that gets compressed to pump the heat that warms your home. But different brands of heat pump come with different refrigerants inside.

Refrigerant choice affects the performance, serviceability, and environmental impact of heat pumps. So let’s go examine the main categories of refrigerant you’re likely to find in your heat pump today:

CFC and HCFC Heat Pumps

  • R-11 (CFC-11)
  • R-12 (CFC-12)
  • R-22 (HCFC-22)

Safety, stability, and ease of manufacture once made CFCs and HCFCs the most popular refrigerants in heat pumps. However, HCFCs are damaging to the ozone layer, and CFCs are extremely damaging. For this reason, both classes of refrigerants were phased down beginning in 1987 under the Montreal Protocol. They also happen to be powerful greenhouse gases. (R-12 is 3,400 times more potent than carbon dioxide as a greenhouse gas).

Nowadays, heat pumps sold in the European Union do not contain CFCs or HCFCs. And since 2015, it’s also been illegal to use CFCs and HCFCs for servicing old equipment.

HFC Heat Pumps

  • R-32 (HFC-32)
  • R-134a (HFC-134a)
  • R-410a (HFC-410a)

After the Montreal Protocol, manufacturers needed a replacement for CFCs and HCFCs. Their answer was HFCs. HFCs are much less damaging to the ozone layer than CFCs or HCFCs. Unfortunately though, HFCs are potent greenhouse gases nonetheless. R-410a, for example, has a global warming potential 2,088 time higher than carbon dioxide.

HFCs have a large share of the heat pump market in Ireland today. However, the European Union is trying to change that with a phase down of HFC consumption. A quota system is currently in place, with the HFC limit falling every year. By 2030, the HFC quota will be 79% below the 2009-2012 baseline. The phase down isn’t exactly going to plan though, as smugglers are running a thriving black market for HFCs in the EU.

Heat pump manufacturers that use HFCs are moving towards R-32. R-32 has a significantly lower global warming potential (675) than R-134a (1,430) or R-410a (2,088). But eventually, R-32 will probably be phased out as well.

Reasons to Avoid HFC Heat Pumps

My advice is to avoid HFC heat pumps where possible. This is not only for environmental reasons, but also because HFC heat pumps will become more and more difficult to service when the EU cracks down on HFC smuggling. You don’t want to find that your heat pump is impossible to fix 10 years from now because the refrigerant refill it is illegal!

If you do choose a HFC heat pump, then R-32 is probably the best option, as it has a lower global warming potential than most other HFCs. So refills are likely to be available for a few decades. On the other hand, R134a and R410a have high global warming potential, and will be phased out sooner.

My second warning is to be weary of heat pump manufacturers and sales people. You will often hear particular HFCs described as “eco-friendly”. It’s true that some HFCs are far less damaging than others. But all HFCs refrigerants are potent greenhouse gases.

To be fair to HFC heat pumps, I should note that they still contribute far less to global warming than burning oil or gas for heat. For example, burning 1,000 litres of oil per year for 20 years releases about 51 tonnes of CO2. Meanwhile, the R-32 refrigerant charge in typical a heat pump is equivalent to around 2 tonnes of CO2. But why risk trouble down the line, when better alternatives are available?

Brands that sell HFC-based heat pumps include Daikin (R-410a and R-32) Samsung (R-32), Mitsubishi/Ecodan (R-32), Panasonic (R-410a), and Stiebel Eltron (R-410a).

HFO Heat Pumps

  • R-1234yf (HFO-1234yf)

HFOs are chemically related to HFCs. The difference is that HFOs quickly break down when released into the atmosphere. So not only are they safe for the ozone layer, but they also have low global warming potential. Hooray!

This fragility of HFOs comes with downsides, however. The first downside is that most HFOs cannot be used in high-temperature heat pumps, as high temperatures would destroy these refrigerants. Secondly, there’s a risk of pollution when HFOs decompose in the environment. This is a relatively minor concern though, as the quantities of HFOs used are likely too small to be detrimental.

Overall, HFOs are likely to be more future-proof than HFCs.

HC Heat Pumps

  • R-290 (propane)
  • R-600 (butane)
  • R-600a (isobutane)

Hydrocarbons (HCs) have excellent properties as refrigerants: They are non-toxic, efficient, and environmentally benign in small quantities. However, they were replaced by CFCs in the 1930s due to flammability concerns.

Technological advances mean that hydrocarbons can now be safely used as refrigerants. Indeed, almost all domestic fridges sold in the EU today use HC refrigerants (usually R-600a).

The heat pump market is also rapidly moving towards HC refrigerants. R-290 is particularly popular, as it works at the ideal temperature range for heat pumps. Heat pumps using HC refrigerants are a future-proof choice as refills should be available long into the future.

Brands that offer heat pumps using HC (R-290) refrigerant include the Valiant, Wolf, Roth, and NIBE.

CO2 Heat Pumps

  • R-744 (Carbon Dioxide, CO2)

CO2 has some great properties as a refrigerant. It’s non-toxic, non-flammable, environmentally benign in small quantities, and stable. The main drawback is the very high pressure required to turn CO2 into a liquid that can be used in refrigeration. This requires stronger materials and results in higher manufacturing costs.

CO2 heat pumps are well suited to high-temperature applications. This can make them a good drop-in replacement for oil boilers using existing radiators, or in houses that use a lot of domestic hot water. CO2 heat pumps have already gained widespread use in Japan, and they are starting to appear in Europe now as well.

My only reservation about CO2 heat pumps is that they are a less well established technology in Europe. This means it could be more challenging to find someone who can service your heat pump, if the need arises. In particular, the properties of CO2 are very different to other refrigerants, so it takes a different skill set to work with this gas. So if you go for a CO2 heat pump, but make sure it’s from a strong brand with a solid warranty. On the other hand, CO2 heat pumps are future-proofed against future environmental regulations.

Mitsubishi/Ecodan already offer a CO2 residential heat pump. Vattenfall is launching a CO2 residential heat pump in the Netherlands and the UK, with expansion to more markets to follow if all goes well. And Enerblue provide commercial-scale CO2 heat pumps.

Summary: What Type of Refrigerant Should You Choose for a Heat Pump?

CodeCategoryGlobal Warming PotentialVerdict
R-410aHFCVery HighAvoid
R-134aHFCVery HighAvoid
R-744CO2LowChoose (but double-check brand quality and warranty)