How efficient is a gas boiler?

The efficiency of a gas boiler can vary depending on factors such as the design of the boiler, its technology, age, and maintenance. The two commonly used metrics to measure boiler efficiency are the Annual Fuel Utilization Efficiency (AFUE) and the Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK) rating. 

1. Annual Fuel Utilization Efficiency (AFUE): AFUE is a measure of the overall efficiency of a boiler over a heating season. It represents the percentage of fuel energy that is converted into heat for space heating. For example, if a gas boiler has an AFUE rating of 85%, it means that 85% of the fuel's energy is used for heating, while the remaining 15% is lost.Modern high-efficiency gas boilers can have AFUE ratings of 90% or higher. These boilers typically incorporate advanced technologies like condensing heat exchangers, which extract additional heat from the combustion gases before they are vented. By recovering more heat from the exhaust, condensing boilers can achieve higher efficiency levels.

2. Seasonal Efficiency of Domestic Boilers in the UK (SEDBUK): The SEDBUK rating is used in the United Kingdom to measure the efficiency of domestic boilers. It represents the annual efficiency of the boiler based on typical domestic usage patterns. SEDBUK ratings are given on a scale from A to G, with A-rated boilers being the most efficient.

A-rated gas boilers in the UK usually have SEDBUK ratings of 90% or higher. However, it's worth noting that SEDBUK ratings were discontinued in 2015, and the UK now uses the ErP (Energy-related Products) directive and labels to assess the energy efficiency of boilers.To ensure optimal efficiency, it's important to properly size and install the gas boiler according to the heating requirements of the building. Regular maintenance, including cleaning and tuning the boiler, can also help maintain its efficiency over time.When considering the efficiency of a gas boiler, it's essential to compare different models and consult their specific AFUE or SEDBUK ratings. Additionally, local regulations and energy standards may influence the minimum efficiency requirements for new boiler installations in your region.