Refrigerant
The refrigerant is the substance that evaporates and liquefies again inside the heat pump, thereby transporting the heat from the source into the house.
- Evaporator: the cold refrigerant absorbs heat from the air, ground or water and evaporates.
- Compressor: it compresses the vapour, which increases the temperature. Electricity is needed here.
- Condenser: the hot vapour releases its heat to the heating water and becomes liquid again.
- Expansion valve: the pressure drops, the refrigerant cools down, and the cycle starts all over again.
A heat pump works like a refrigerator in reverse. Inside, a refrigerant circulates. It evaporates even at low temperatures, such as the ground temperature of around 2 °C, absorbing heat in the process. The compressor brings the vapour to a higher pressure and temperature level. In the condenser, the refrigerant releases the heat to your heating water and becomes liquid again. Then the cycle starts all over again.
Why you should care about the refrigerant
Many refrigerants are fluorinated gases with a high global warming potential (GWP). In normal operation, the refrigerant remains in a closed circuit; klimaaktiv emphasises that leakage is the exception. Nevertheless, klimaaktiv recommends choosing systems with the lowest possible GWP. According to the guide, the refrigerant also influences the maintenance costs.
Natural refrigerants
According to klimaaktiv, refrigerants with a very low GWP (below 10) include R290 (propane) and R744 (CO2). EU Regulation 2024/573 gradually restricts fluorinated gases in new heat pumps, meaning natural refrigerants are becoming increasingly important.
What you can do
- Ask in the quote which refrigerant is used and how much of it is in the unit.
- When it comes to the design, pay attention to whether refrigerant pipes are routed inside the house (split) or the circuit remains closed in the outdoor unit (monobloc).
Sources
- klimaaktiv Wegweiser zur guten Installation von Wärmepumpen (klimaaktiv Guide to Good Installation of Heat Pumps, BMK, 2020) (accessed on 4 October 2026)
- Regulation (EU) 2024/573 on fluorinated greenhouse gases (EUR-Lex) (accessed on 4 October 2026)
- klimaaktiv: So läuft Ihre Wärmepumpe rund. Tipps für die Planung und Installation (klimaaktiv: How to Keep Your Heat Pump Running Smoothly. Tips for Planning and Installation, BMK, 2024) (accessed on 4 October 2026)