Boiler Efficiency & Savings Calculator
Calculate your annual boiler running cost and estimate savings from upgrading to a modern condensing boiler. Based on your current boiler age and efficiency rating.
Boiler Replacement Guide
Boiler Efficiency Ratings
Modern condensing boilers (all new domestic installations since 2005 in the UK) achieve SEDBUK efficiency ratings of 86–93%. The condensing process captures heat from exhaust gases that older boilers waste — hence the plastic condensate drain pipe you see on modern boilers. Pre-2005 boilers are typically non-condensing and run at 60–75% efficiency. An old G-rated boiler converts only 65p in every £1 of gas to useful heat; a modern A-rated condensing boiler converts 90p or more.
True Cost of a New Boiler
A new gas boiler (combi, system, or regular) installed costs £2,000–4,500 depending on type, size, and installation complexity. A combi boiler replacement in a straight swap (same location, same pipes) is the cheapest option. Converting from a regular/system to combi requires removing the hot water cylinder and header tank, adding £500–1,000. Worcester Bosch, Viessmann, and Ideal Logic are consistently rated highest for reliability. Parts availability and service network matter more than price f
Boiler Plus Regulations
Since April 2018, all new boiler installations in England must include a 'time and temperature zone control' — separate programmable controls for heating and hot water and, for combination boilers, one or more of: load compensation, weather compensation, flue gas heat recovery, or smart controls. This is the 'Boiler Plus' regulation. Smart thermostats (Nest, Hive, Tado) are the most common compliance route, and they deliver genuine energy savings of 10–20% through intelligent scheduling and occu
Government Grants
The Boiler Upgrade Scheme (England and Wales) does not cover gas boiler replacements — it provides grants for heat pumps (£7,500) and biomass boilers (£5,000). The ECO4 scheme may fund a new boiler or insulation for households on certain benefits — eligibility is determined by household income, current energy efficiency rating, and benefit status. Check the Government's 'Help for Households' website or use an eligibility checker before getting quotes. Local authorities sometimes have additional
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