Condensing boilers are the most energy-efficient boilers on the market today. They use less fuel and have lower running costs than other boilers. They achieve this high level of efficiency by extracting heat contained in the combustion gases, which would otherwise be lost to the atmosphere. Old, conventional boilers have an efficiency rate up to 60%, which means that they convert 60% or less of their fuel into heat, while the efficiency of new condensing boilers can be above 90% (A-rated). This means huge energy savings and significant cuts on your CO2 emissions and gas bills.