In the UK domestic market, it has been compulsory for all new gas central heating boilers installed to be condensing boilers. While a conventional boiler will usually just project any excess heat from its flue into the atmosphere, a condensing boiler will recover as much of this waste heat as possible and put it to much more efficient use. This is because a condensing design uses an extra-large heat exchanger, which, during the condensing process, maximises heat transfer from the burner. The heat given by the flue gases can then be recovered by the heat exchanger, effectively recycling the energy. Condensing boilers therefore have a better operating efficiency than a conventional non-condensing design.

There are two main benefits to gain from using a condensing boiler: lower energy bills and a reduced carbon footprint. As condensing boilers are so much more efficient than their conventional counterparts when turning fuel into usable heat, less fuel is required overall to heat both water for heating and “domestic use”. The fuel efficiency in condensing boilers is also much better and significantly reduce carbon emissions.