What is a high efficiency condensing boiler?

Condensing boilers get their name because they enter what is called "condensing mode" periodically. In other words, they start to extract heat from the exhaust gases that would otherwise escape through the flue, in the process turning water vapour from the gas back into liquid water or condensate.

A condensing boiler captures much more usable heat from its fuel than a non-condensing boiler. Its high operating efficiency is made possible by the design of the condensing boiler's larger - or sometimes dual - heat exchanger.

The heat exchanger makes sure that as much heat as possible is transferred from the boiler's burner - and as little as possible lost in gases through the flue.

There are two types of condensing boiler: regular and combination. Regular condensing boilers heat your hot water through a hot water cylinder. Combination condensing boilers give you instant hot water without the need for a cylinder.

Please bear in mind that not all home heating systems will be compatible with a combination boiler. A qualified installer will tell you which type of condensing boiler, regular or combination, is most suitable for your home.

If your boiler is 15 years old or more then it could be a G rated boiler. You can find out if your boiler is G rated by checking the list here. Replacing an old G rated boiler with a new A rated condensing boiler and a full set of heating controls can save up to a quarter on your heating bills straight away and up to 1,300kg of CO₂ year. If your boiler is younger than 15 years then it is likely to be more efficient so will save you less if you replace it.

If your boiler is newer then it may well be in a higher energy efficiency band. Below are typical savings which can be achieved by replacing boilers with new A-rated condensing models and installing a full set of heating controls:

Old Boiler Rating	Annual Saving (£/yr)	Annual Saving (kgCO2/yr)
G ( < 70%)	£235	1,260
F (70% - 74%)	£150	800
E (74% - 78%)	£110	575
D (78% - 82%)	£70	375

Save up to a quarter on your heating bills by replacing your boiler and heating controls

Condensing boilers can be easily fitted to most new and old heating systems, ask your installer for more details.

Did you know?

If everyone in the UK with gas or oil central heating installed a high efficiency condensing boiler with full sets of heating controls, we would save enough energy to heat nearly 1.9 million homes for a whole year and save around 6.7 million tonnes of CO_2.

Savings assumptions