Condensing boilers get their name from their tendency to form water due to the rapid cooling of flue gases. This is the result of a larger or an additional heat exchanger, which traps as much heat as it can and returns it to the boiler. Under current regulations, boiler replacements after April 1, 2005 must be a condensing boiler.
In addition to the heat exchanger, the condensation itself helps trap precious heat. Due to the acidic properties of the condensate, the boiler must be made out of corrosion-resistant metals such as stainless steel or aluminium. Any condensate build-up is drained via an outlet to lessen the risk of corrosion.
Authorities are urging the public to switch to Grade-A condensing boilers. According to the Seasonal Efficiency of Domestic Boilers in the U.K. (SEDBUK), these boilers have a rated efficiency of over 90 percent. A single-family house can save almost £500 if it switches from a Grade-G boiler, with a SEDBUK of below 70 percent.