Heat pumps work like a refrigerator in reverse. They extract heat from the environment (air, water, or the ground) and make it usable for heating purposes. The proportion of electrical energy consumed is significantly lower than the proportion of environmental heat utilized.

1. A heat exchanger connects the heat pump to the heat source. This can be an outdoor unit with a fan to extract heat from the air, or it can be a geothermal heat exchanger, a groundwater well, or another source. A very cold liquid flows through this heat exchanger. It heats up until it reaches the same temperature as the heat source and evaporates in the process. Evaporation extracts a significant amount of energy from the heat source—in everyday life, we’re familiar with this effect from sweating, where evaporating sweat cools the skin. 
2. The resulting gas flows into a compressor, which increases the pressure. The increased pressure also raises the temperature. The gas is now warm enough to be used in the heating system. 
3. However, the gas is not fed directly through the radiators; instead, it transfers its heat to the heating water in a second heat exchanger. As a result, the gas condenses again and becomes a liquid. 
4. In the final step, the liquid is expanded through a valve. As this happens, both the pressure and temperature drop. The liquid is now colder than the heat source again. The cycle can then begin anew.

Electricity is primarily used in this process to power the compressor, as well as for smaller pumps. The heat comes mainly from the environment. In this way, up to four kilowatt-hours of heat can be generated from one kilowatt-hour of electricity. 

• They use heat from the environment to generate up to four times more heat than they consume in electricity.
• By utilizing ambient heat, they make optimal use of the electricity they consume. This saves costs and reduces CO₂ emissions.
• As the share of renewable energy in the electricity mix increases, CO₂ emissions will automatically decrease in the future. By using green electricity, these emissions can already be further reduced today.
• Heat pumps can be used for both heating and cooling buildings.
• Modern heat pumps operate very quietly. 

Heat pumps are particularly well-suited for locations where there is sufficient space for the outdoor unit, which extracts heat from the environment. This is especially true in less densely built-up neighborhoods. In municipal heating plans, these neighborhoods are designated as areas for decentralized heating. Modern heat pumps can be used in both new and existing buildings. 

A heat pump is particularly efficient when the temperature difference between the environment and the heating system is small. This is achieved either by using a particularly warm heat source—such as wastewater or waste heat from data centers—or by operating the heating system at low temperatures. 

For this reason, heat pumps were often used in new construction projects and with underfloor heating systems, since the required temperatures are low in these applications. However, modern heat pumps are also capable of generating higher temperatures, so their use in older buildings with traditional radiators is generally no longer a problem. Nevertheless, it’s worth checking whether a hydraulic balancing can be performed or whether individual radiators should be replaced. This often makes the heating system even more efficient.