What is a condensing boiler?

Condensing boilers are designed for enhanced energy efficiency, which is what makes them a lot more popular than the older style heating systems. Non-condensing boilers tend to have efficiencies of around 75%, which is wasting hundreds of pounds every year on heating bills.

However, condensing boilers operate at increased efficiency, pushing towards the 87% mark and more. This is all because of the way heat is extracted from waste gases, so less is lost in the flue and instead converted into heat for the home.

In condensing boilers there are two significant ways the amount of heat used is enhanced. First of all, heat rises upwards into the exchanger. Once it reaches the top it’s diverted into a second exchanger to capture more heat. Heat exiting the flue is only at a temperature of 55°C, rather than around 180°C in a normal boiler.

Combi boilers are a form of condensing boiler and extremely popular in UK households. This is mainly for two reasons; they’re small and able to fit in the kitchen cupboard or on a wall, and can provide hot water on demand, with no need for a water storage tank.

Many of the older boilers will have a storage tank fitted in the loft or airing cupboard taking up plenty of room. Replacing this system with a combi is becoming more popular to open up the space and save up to £300 a year on heating bills.

The below table shows what can be saved by replacing your inefficient heating system:

Old boiler rating Annual saving Carbon dioxide saving per year
G (<70%) £300 1,220kg
F (70-74%) £200 810kg
E (74-78%) £150 610kh
D (78-82%) £105 420kg