Heating System Efficiencies
Previously, boilers were graded using only their manufacturer's own laboratory tests. However since the introduction of the UK SEDBUK system, ratings have become more reliable, simple and consistent.
The SEDBUK rating works by measuring how much fuel used by a boiler is converted to heat under a variety of typical running conditions. The percentage measured indicates the annual efficiency the boiler will achieve in typical household conditions.
The ratings are categorised from A to G, with A representing the highest efficiency of over 90%, and G being the lowest below 70% efficiency. The SEDBUK rating is now highly recognised and offers a way to independently compare boiler specifications. Through competitive pressures between manufacturers, this rating system has lead to great strides in increasing efficiencies.
Regardless of boiler efficiency, the emissions and energy wastage from heating domestic hot water could possibly be much higher, as in many cases heating zones are not installed or working correctly allowing the whole house to be heated (particularly in spring and autumn) when the only demand is hot water for showers.
Additionally, the pipe-run between the boiler and the cylinder is often poorly lagged and in many houses is very wasteful of energy.
So poor is this overall performance, that some solar simulation packages use a default boiler efficiency of just 55% when calculating water heating compared with 80% for the heating system.