Boiler Efficiency Ratings: A Comprehensive Guide
Boiler efficiency ratings are a crucial consideration for renters, homeowners, landlords, and businesses looking to optimise energy use, reduce heating costs, and minimise environmental impact. In the UK, where heating accounts for a significant portion of household and commercial energy consumption, understanding boiler efficiency ratings is essential. This article explores boiler efficiency, how it is measured, the different rating systems, ways to improve efficiency, and the environmental and financial benefits of high-efficiency boilers.
What is Boiler Efficiency?
Boiler efficiency refers to how effectively a boiler converts energy from fuel into heat. It is measured as a percentage, with a higher percentage indicating greater efficiency. Ultimately, a highly efficient boiler requires less fuel to produce the same amount of heat, leading to reduced energy bills and lower carbon emissions.
Boiler efficiency depends on several factors, including:
- The type of boiler (combi, system, or conventional)
- The age and condition of the boiler
- The type of fuel used (gas, oil, LPG, biomass)
- The quality of maintenance and servicing
How is Boiler Efficiency Measured?
Boiler efficiency is determined through standardised tests that measure how much of the fuel’s energy is converted into usable heat. In the UK, two main rating systems assess boiler efficiency: the Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK) and the ErP (Energy-related Products) Directive.
SEDBUK Ratings
The SEDBUK rating system was introduced by the UK government to provide a standardised measure of boiler efficiency. Initially, boilers were rated from A to G, with A-rated boilers being the most efficient (over 90%) and G-rated boilers being the least efficient (below 70%). In 2009, SEDBUK changed to a percentage-based system, where efficiency is expressed as a percentage, making it easier to compare boilers.
What Is The Energy Efficiency Rating of My Boiler?
Search for your make and model below to find the efficiency of your boiler based on the SEDBUK ratings.
ErP Ratings
The ErP (Energy-related Products) Directive is an EU-wide regulation designed to improve the efficiency of energy-consuming products, including boilers. Introduced in 2015, it provides an energy efficiency rating from A+++ (most efficient) to G (least efficient). The ErP system includes considerations such as standby power consumption and emissions, offering a broader assessment of efficiency.

Factors Affecting Boiler Efficiency
Several factors influence the efficiency of a boiler:
1. Age of the Boiler
Older boilers tend to be less efficient due to wear and outdated technology. A 15-year-old boiler may operate at 70% efficiency, meaning 30% of the energy is wasted. Modern condensing boilers can reach efficiencies of over 90%.
2. Type of Boiler
- Combi Boilers: Highly efficient and compact, providing hot water on demand without a storage tank.
- System Boilers: Require a hot water cylinder but are more efficient than conventional boilers.
- Conventional Boilers: Require both a cold water tank and a hot water cylinder, typically less efficient.
3. Fuel Type
- Gas Boilers: Generally the most efficient and widely used in the UK.
- Oil Boilers: Suitable for off-grid homes but less efficient than gas boilers.
- LPG Boilers: Offer flexibility but have higher fuel costs.
- Biomass Boilers: Use renewable energy sources but require more maintenance.
4. Boiler Controls and Thermostats
Modern heating controls, such as smart thermostats, weather compensation, and load compensation, can significantly improve boiler efficiency by optimising energy usage.
5. Maintenance and Servicing
Regular servicing ensures the boiler operates efficiently, preventing breakdowns and improving longevity.







How to Improve Boiler Efficiency
Improving boiler efficiency can reduce energy bills and lower carbon footprints. Here are some key ways to enhance boiler efficiency:
Upgrade to a High-Efficiency Boiler
Replacing an old, inefficient boiler with a modern A-rated condensing boiler can result in significant savings. A condensing boiler recovers heat from exhaust gases, improving efficiency.
Use a Smart Thermostat
Smart thermostats allow precise control over heating, preventing energy waste by only heating when necessary.
Install Thermostatic Radiator Valves (TRVs)
TRVs help control the temperature in individual rooms, reducing unnecessary heating in unoccupied areas.
Bleed Radiators Regularly
Trapped air in radiators reduces efficiency. Bleeding radiators ensures they heat up evenly and efficiently.
Improve Insulation
Better insulation, such as loft insulation, cavity wall insulation, and draught-proofing, reduces heat loss, making the boiler work less to maintain temperatures.
Schedule Regular Servicing
Annual servicing by a Gas Safe registered engineer ensures the boiler operates at peak efficiency and identifies potential issues early.
Environmental and Financial Benefits of Efficient Boilers
An energy-efficient boiler offers several advantages:
1. Lower Energy Bills
A high-efficiency boiler requires less fuel to heat a home, leading to lower heating costs.
2. Reduced Carbon Emissions
Efficient boilers emit less CO₂, contributing to a greener environment and helping the UK meet carbon reduction targets.
3. Increased Property Value
Homes with energy-efficient boilers and heating systems are more attractive to buyers and may command a higher market value.
4. Government Incentives and Grants
Schemes such as the ECO (Energy Company Obligation) grants may help cover the full cost of upgrading to a high-efficiency boiler.
Conclusion
Boiler efficiency ratings are a crucial consideration for anyone looking to optimise home heating. By understanding how efficiency is measured, the impact of various factors, and ways to improve performance, homeowners can make informed decisions that lead to cost savings and environmental benefits. Upgrading to a modern, energy-efficient boiler, implementing smart heating controls, and ensuring regular maintenance can maximise efficiency and sustainability, making heating systems more effective and economical in the long run.