A combi (combination) is the most common type of heating system, fitted in many UK properties. As the name implies, it performs the dual tasks of running your central heating, and also provides on-demand hot water, thanks to the built-in water heater unit. Unlike other types, a combi doesn't require you to have a separate hot water tank. It is therefore ideal when you have limited space, or if you wish to free space by getting rid of your old water tank. Since 2010, all combi units much reach at least 'A' efficiency rating, meaning this is a good choice for saving money. Around 70% of UK homes rely on combis for their heating and hot water supply. Other benefits include a cheaper installation, as there are fewer parts, and less risk of failure from freezing pipes, electrics, or issues with a separate tank.