Most types of boiler can be high efficiency or 'condensing' boilers. There are high efficiency combination boilers, system boilers, or traditional open vent boilers. The term 'condensing' or high efficiency applies to the technology which is used. This means the boiler recovers more heat from the amount of gas that is burnt thereby making it more efficient than conventional boilers.

By recovering and using heat that would otherwise be lost up the flue, the best high efficiency boilers can operate with seasonal efficiencies in excess of 90%. Although high efficiency boilers require a higher initial investment, they are very economical, and can repay the extra initial cost in fuel savings.

If your existing boiler is more than 15 years old, replacing it with a high efficiency boiler could save you as much as 35p in every £1 on the gas used for heating and hot water.