What are Condensing boilers?
Most types of boiler are also available as high efficiency or "condensing" boilers. There are high efficiency combination boilers, system boilers, or conventional boilers. The term `condensing' or high efficiency applies to the technology which is used to maximise boiler efficiency to use less fuel for more heat.

A condensing boiler is a high efficiency modern boiler that incorporates either a larger heat exchanger or even a second heat exchanger. It produces lower flue gas temperatures, lower flue gas emissions, and reduced fuel consumption . It typically converts more than 88% of the fuel used into useful heat, compared to, typically, 78% for modern conventional types.

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%. Recovering the heat from the flue reduces the temperature of the flue gases to a point where water vapour produced during combustion is 'condensed out'. Thus the name high efficiency condensing boiler. A side effect is that this 'condensed out' water, known as condensate, which is acidic, has to be piped away to a drain or soakaway. All condensing boilers will produce ‘pluming’ from the flue terminal which appears as steam. This pluming can drift into neighbouring property causing annoyance and possible condensation on window glass or frames so careful consideration should be given to siting of the flue terminal especially if it may effect neighbouring property.

Although high efficiency boilers require a higher initial investment, they are very economical, and repay the extra initial cost in fuel savings.

A condensing boiler can work at over 90% efficiency. For further information on boiler efficiency click here

New regulations came into effect in April 2005, whereby new boilers will have to be high-efficiency A and B-rated condensing boilers. For more information click here

The Energy Efficiency Partnership for Homes have produced the following information: Benefits & Myths about Condensing Boilers