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Why CO2/R744 Is Used As A Refrigerant For Heat Pumps

The choice of refrigerant is a critical factor in determining the performance, longevity and environmental impact of a heat pump. We wrote before about the effect or refrigerant choice on heat pump performance and, alongside ambient conditions, heating system performance and build quality, refrigerant choice makes an enormous difference.

With rising concerns about the dangers of F-Gas and PFAS chemicals, owners and regulators are looking towards natural refrigerants. REACH regulations and recent votes to accelerate F-gas phase out in Europe are only adding to the move. The retail refrigeration sector made the move to natural refrigerants 10 years ago and has paved the way for the heating sector to follow. More and more natural refrigerant heat pumps are appearing on the market every week. 

At Clade, our flagship heat pumps are CO2 heat pumps. Here we’ll discuss why that is.

Why Use CO2 As A Refrigerant In Heat Pumps


  • CO2 is environmentally friendly: CO2 is a natural refrigerant that does not deplete the ozone layer and has a minimal contribution to global warming, unlike some other refrigerants like CFCs and HCFCs which are 100’s or 1000’s of times more potent..
  •  CO2 is energy-efficient: CO2 has specific thermodynamic properties, which means that it can efficiently transfer high temperature heat with less energy consumption compared to some other refrigerants.
  • CO2 is safe: CO2 is non-flammable, non-toxic, and non-explosive, making it a safe refrigerant to handle and operate.
  • CO2 is widely available: CO2 is widely available and can be easily sourced, making it a cost-effective refrigerant with a secure supply chain compared to some other synthetic refrigerants that may be more expensive or difficult to obtain. These synthetic refrigerants are also likely to face more and more regulatory restrictions in the coming years, whereas CO2 will not. 
  • CO2 heat pumps have a large Delta T. CO2’s wider temperature difference between flow and return (typically 40⁰C) means you can have smaller distribution pipes, valves, fitting, bracketry and lagging. That saves money, electrical energy, heat loss and space. 
  • CO2 can generate high temperatures. CO2 heat pumps can generate temperatures high enough for domestic hot water as well as space heating. There’s no need for different specialist heat pumps, saving money. 

The energy transition, and the decarbonisation of heat in particular, is a massive challenge for organisations. The decisions made now in terms of capital allocation will have big implications over the next twenty to thirty years in terms of regulatory burden, emissions and costs. 

Heat pumps are not a controversial technology. In fact, among those that know their onions, they are almost unanimously regarded as the best replacement for existing heating systems. Previously, one of the main issues with them was the expensive and environmental impact of the refrigerants but, now that the technology has advanced and CO2 is viable, this is no longer the case. 

CO2’s thermodynamic properties, safety and availability make it the ‘natural’ choice in more ways than one. Its total cost of ownership is also likely to be lower than alternatives.

It does come with one specific engineering challenge –  a lower return temperature is required, but with good design practice these can easily be overcome. 

An example system schematic is here and our white paper on CO2 is here