Heat pumps are increasingly gaining popularity as the world is moving towards low-carbon energy systems. Use of heat pumps for domestic heating and hot water is widely seen as a sustainable option, and a step further from conventional fuel dependence. In spite of being ‘green’ in terms of carbon-pollution, there is a need to move towards low GWP working fluids in heat pump systems to ensure minimal impact to the environment. Low GWP fluids and mixtures have been emerging in the light of sterner legislations being introduced to limit, if not to totally prevent, further use of high GWP fluids. Replacement fluid has to satisfy a number of criteria, primarily to perform similarly to the original fluid. We have compared high and low GWP fluids, as well as several mixtures, as working fluids in the same operational scenario. Low GWP fluids are fundamentally different from conventionally used one, but their performance has some promising features.