This paper highlights the implications of various gas coolers on the CO2 heat pump water heating system and how it can be applied in building for energy efficiency purpose. These highlights focus on different gas coolers that have been used and how effective they have been. However, the gas cooler is made possible due to the fact that the refrigerant is working above the condensation state. Carbon dioxide has been the only refrigerant that can replace the about to be-phased-out refrigerants like CFCs, HCFCs, and HFCs. In this paper, advantages of different gas coolers such as; shell and tube, tube in tube, plate and fin, microchannel etc. gas coolers are highlighted and also focus on its implications on building in the area of energy management in bathing, cooking and washing