There are many reasons why heat transfer and heat exchangers play a key role in the reduction of greenhouse gas (GHG) emissions. Reduction of the final energy consumption and improvement of the power conversion efficiency mean less prime energy consumption, resulting in overall GHG emission reduction. A fuel cell cycle is a promising power conversion method, with high efficiency and producing only water or water steam by using hydrogen. Some renewable energy sources, e.g., biomass and solar energy, have net zero GHG emissions or have no GHG emissions at all. In all these aspects, heat transfer and heat exchangers are very important. In addition to these indirect effects, heat transfer and heat exchangers can also have direct effects on GHG emissions in various situations. In this paper, several examples are reviewed and illustrated, to demonstrate why heat transfer and heat exchangers are important in the development of energy systems generating low emissions of GHG. It is found that the attempt to provide efficient, compact and cheap heat transfer methods and heat exchangers is a real challenge for research. In order to achieve this, both theoretical and experimental investigations must be conducted, and advanced modern techniques must be adopted.