Condensing boilers – Gas and Oil Fired

Condensing central heating boilers are the most energy efficient boilers available.

They can be up to 10% to 15% more efficient than a modern conventional boiler and up to 30% more efficient than older boilers so the energy saving and the impact on your fuel bills can be significant. They cost a little more but the extra cost will normally be recovered in fuel savings in 2 to 4 years.

See the SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) website for some useful facts and figures.

Conventional boilers lose a substantial amount of heat with the products of combustion. Condensing boilers achieve the extra energy efficiency by recycling the hot exhaust to pre-heat the cold water coming in. This is done through a larger heat exchanger setup. So instead of sending all that heat out of the flue it is reused and is condensed into liquid.

The more efficient the boiler is, the less fuel it uses, the less carbon dioxide it produces and the less it costs to run.

Current Regulations:

All gas boilers (and from 1 April 2007 – all oill boilers) fitted in both new and existing homes must be condensing boilers with either an ‘A’ or ‘B’ efficiency rating (A= greater than 90%, B= 86%-90%).

There are exceptional circumstances (for example where it is not practical or economic) when a non-condensing boiler can be fitted.

Features of condensing boilers compared to conventional boilers?

  • the exhaust gases are relatively cool and a fan is needed to compensate for the lower convection flow
  • the condensation process produces a liquid which is acidic (due to sulphur and nitrogen impurities), which requires the use of special materials and the addition of a fluid draining system
  • the exhaust will appear as a continuous plume of steam
  • fitting a condensing boiler to an existing system will normally require the system to be power-flushed