A condensing oil boiler has been designed to help improve energy efficiency.
This is done by converting water vapour condensation into heat; condensing oil boilers are able to recover some of the lost heat from waste gases.
A condensing oil boiler will begin to burn when lit. As it does so, it inputs the heat from the burner into a primary heat exchanger. The hot air travels through the heat exchanger and is kept here for as long as possible to increase the temperature. It will then take this heat away to your radiators or underfloor heating.
Condensing boilers are designed to recover more heat before it is lost. Condensing boilers are great at recycling that heat to increase the temperature of the cool water that returns.