Condensing Boilers

Condensing Gas Boilers
Gas Boiler - Condensing high efficiency combi boiler

Condensing gas boilers function at extremely high efficiency levels because of their design.

Condensing boilers are designed to preheat water from the mains cold water tap before it is heated by the boiler’s burner.

The water is already warm so takes much less time to heat, saving on both energy and heating costs.

The condensing functionality of a boiler is a feature rather than a specific boiler type. As such, both regular boilers and combi boilers can have this functionality.

Conventional Gas Boilers

Regular gas central heating boilers work in a straightforward fashion –  there has to be enough energy generated to heat the cold water in a large tank.

By heating water via a heat exchanger – fuel, or gas, is burned and the heat passes through a compartment where a percentage heat is transferred to cold water.

This hot water is used to heat your radiators or for your hot water taps. The remainder of the heat escapes from the boiler.

This can be very expensive – especially if you only want to heat water for your hot taps, for example, as it means heating up your whole central heating system.

Energy efficient design of condensing boilers

A condensing boiler partially heats cold water before it enters the burner by means of a heat exchanger.  Technically a thermal transfer of heat occurs from the exchanger to the water, warming it up before it reaches the boiler.

Condensing boilers are A rated. This means that they function at 90% efficiency or above. They use less energy, which means that less harmful carbon dioxide emissions are released into the environment, heat your water more effectively so that your gas bills are reduced.

As much as 60% of heating costs are used to heat your boiler for hot water or warmth in the home.

Domestic Gas Boiler Efficiency Grades

SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) are the

Energy Performance Certificate for Gas Boiler
Gas boiler energy-efficiency ratings

advisory organisation responsible for the grading of boilers in England, Scotland & Wales.

The diagram shows the range of traditional energy-efficiency ratings for conventional boilers and central heating systems.

All gas condensing boilers function at over 90% efficiency, This is also the mandatory level for any new boiler installed in the UK.

Domestic Gas Boilers &  Energy Performance

The body which determines a boiler’s grading is SEDBUK (Season Efficiency of Domestic Boilers in the UK).

Boiler and central heating performance contributes to the overall energy performance of your property and is included in any Energy Performance Certificate (EPC) or Report.

Boiler performance is measured as a percentage although the European Grading method (A-G according to energy usage performance) is also often included for consistency.

The energy efficiency of gas boilers (the free boilers available in the UK are gas boilers) is assessed on a variety of factors including –

  • seasonal conditions
  • heating usage patterns
  • housing occupancy
  • boiler storage conditions
  • where boiler is located
  • boiler insulation

Other factors deemed to affect the energy efficiency of boilers such as climate and the age of a boiler are also taken into account when assessing a boiler’s performance.

The boiler rating system is designed to be a fair and accurate method of determining boiler efficiency, regardless of manufacturer.

If you are unsure about your boiler or its energy rating you can get it surveyed by a Domestic Energy Assessor. The assessor will come to your home and determine its energy efficiency rating.

How much can I save?
Annual savings
Comparison of typical A Grade condensing boilers compared to older less efficient boilers
Boiler Type Boiler
Flat Bungalow Terraced Semi-detached Detached
Condensing A Grade Boiler 99%  £186  £234  £242  £270 £368
Heavy weight 55%  £308  £393  £408  £458  £634
Light weight 65%  £266  £338  £350 £393  £542

Cost of replacing your boiler

Find out if you qualify for a free boiler replacement here – Free Boilers

Information resources

Condensing boilers

New Boiler Cost | Combi Boiler Finance