The use of environmental energy to supply heating results in less carbon dioxide emissions. Also the emissions from the electricity generation are steadily decreasing. Therefore, heat pumps are a key heating technology for the future. On the other hand, heat pumps still primarily use refrigerants that are harmful to the environment. Now researchers at Fraunhofer ISE, however, have developed a climate-friendly alternative, which uses propane, a natural gas. The greenhouse gas potential is about 500 times less than conventional refrigerants and thus extremely low. Another advantage is that the new brine-to-water prototype requires only one fourth of the refrigerant compared to conventional heat pumps available on the market at the same power. A propane heat pump based on this development would be the first-of-a-kind in Germany that is permitted in interior spaces of residential buildings without implementing additional safety measures. This new technology shall now be improved upon. For the heat pump industry, new refrigerants are especially important: As of January 1, 2020 first bans on harmful refrigerants take effect in the European Union.