Last edited 30 Aug 2021

Boiler efficiency

According to the Non-domestic building services compliance guide, 2013 edition, published by HM Government, ‘boiler efficiency’ means:

…the energy delivered by the water as it leaves the boiler (or boilers in multi-boiler installations) to supply the heat emitters, divided by the energy (based on gross calorific value) in the fuel delivered to the boiler, expressed as a percentage. It is an expression of the boiler’s performance and excludes energy used by boiler auxiliary controls, pumps, boiler room ventilation fans, mechanical flue extraction fans and fan dilution systems. The boiler efficiency is measured according to the standards that are used to demonstrate compliance with the Boiler Efficiency Directive.

Rules of Thumb, Guidelines for building services (5th Edition) BG 9/2011, by Glenn Hawkins, published by BSRIA in 2011, defines boiler efficiency (%) as: ‘…the energy delivered by the water as it leaves the boiler to supply the heat emitters / the energy (based on gross calorific value) in the fuel delivered to the boiler.’

‘Seasonal boiler efficiency (%) is a weighted average of the efficiencies of a boiler at 15%, 30% and 100% of the boiler output.’

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