Gas heating system is a general term that covers all types of heating systems that are fired by natural gas. This includes gas boilers as well as larger gas heating boilers. Gas boilers is a specific types of gas heating system that is often available in a compact form and is installed directly in the living space. Gas boilers can be designed as combi-boilers (for heating and hot water) or as pure heating boilers. The main difference lies in the design and integration into the heating system of the building.