Adoption of heat pumps has been slow, with people citing the costs and complexities of swapping from gas.  

Issues can include high heat losses through buildings, pipework, and emitters sized for a boiler system and finding the necessary space for installation inside and outside.   

These issues are easily addressed in new buildings but can present hurdles to retrofitting.  Installing a propane heat pump (Refrigerant R290) removes some of these issues but does have its own challenges. 

Pros of Propane R290 Heat Pumps 

1. Global Warming Potential (GWP): the refrigerants' low GWP of three and zero Ozone Depletion Potential (ODP) make it an eco-friendly option to synthetic refrigerants.  Being a "natural" refrigerant, it is exempt from F-gas regulations.
2. Temperature Output: R290 can produce hot water at 65°C+ while maintaining a Seasonal Coefficient of Performance (sCoP) over 3, effectively being 3 times more efficient than a gas boiler.  This performance means R290 heat pumps suit existing LTHW swap-outs, including domestic hot water generation.
3. Low Ambient Temperature Use: R290 heat pumps can continue to produce water at 65°C even at ambient temperatures as low as -25°C. 
4. Reduced Refrigerant Charge and Pressures: Efficient heat transfer properties allow lower refrigerant volumes, further reducing costs and environmental impact.  Compared with other refrigerants, the lower system pressures mean it is less likely to leak. 

Cons of Propane R290 Heat Pumps 

1. Flammability: As a hydrocarbon, R290 is highly flammable, citing the heat pump must be considered, and appropriate safety measures must be followed.  However, this should be considered against the fact that many people have a larger volume of propane next to their gas BBQ.
2. Regulatory Restrictions: Limits on charge mass within buildings are currently restricting the capacity of smaller split-type systems to about 8kW.  However, larger commercial systems, where the refrigerant is external, are not affected with cascade products available approaching 1MW. 
3. Cost of Implementation: Safety features like leak detection, more robust components and enhanced training can increase capital costs. 
4. Limited Market Penetration: The race to develop these heat pumps has meant that most manufacturers now offer heat pumps with R290; however, these are still relatively new to the market with no real-world installation near the anticipated 20-year life.  Many market-leading manufacturers are still only offering small-scale/domestic-style systems. 
5. General Heat Pump Issues: The availability of existing electrical capacity, lack of external plant space and noise limitations, which affect traditional heat pump systems, still apply to R290 heat pumps and must be considered. 
6. Maintenance Space: The required space around the units is slightly larger.  This will be for larger component sizes and also increased airflow requirements. 
7. Noise: Comparing market-leading product noise information, propane units can be louder than alternative R32 heat pumps  

The implementation of propane heat pumps should be on a case-by-case basis.  Aspects such as noise and available roof space will drive the decision on whether they can be installed in a building.  They are another useful technology that should be considered for designing decarbonised heating systems.