55% of your energy bills is spent on heating.

According to the Energy Saving Trust:  “Heating accounts for about 55% of what you spend in a year on energy bills, so an efficient boiler makes a big difference.”   The biggest reason for modern combi boiler efficiency is down to condensing boiler technology.

Modern condensing boilers are normally 90-94% efficient. Boilers that are more than 15 years old can be as little as 60% efficient. What does boiler efficiency mean? A boiler’s ‘energy efficiency’ is the percentage of the total energy used by the boiler to supply useful heating to your home. For a modern boiler with 95% efficiency, 95% of the energy used by the boiler goes to heating the home, only 5% is lost through the flue. For a very old boiler with 60% efficiency, only 60% of the energy used by the boiler goes to heating the home, a whole 40% is lost through the flue to the atmosphere.

As a good rule of thumb for non-condensing boilers assume:

  • Over 25 years old: 60% efficient
  • 20 years old: 70% efficient
  • 15 years old 80% efficient
  • 10+ years old 85% efficient

Average Annual Energy Costs for different types of Boilers:


Type of BoilerEfficiencySemi-DetachedDetachedFlat
Modern Condensing Boiler90%-95%£720£1150£500
Non-Condensing Boiler75%-78%£850£1310£700
Old Back Boiler (Light Weight)60%-65%£1020£1450£800
Old Back Boiler (Heavy Weight)50%-55%£1260£1780£850
Categories: boilers

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