How Condensing Boilers Work
A boiler utilises fuel or electricity to heat water for central heating and domestic hot water production. Most modern boilers operate only when called upon by the heating or hot water system and have an internal thermostat to guarantee controllable water temperatures at all times.
Boilers which use fuel (rather than electricity) incorporate a burner for the combustion of the fuel and a heat exchanger to transfer the heat from combustion to the water to be heated. In modern systems, a pump is used to circulate the water through the boiler and around the rest of the heating and hot water system.
Non-condensing boiler operation
In conventional boilers, such as the one in the above diagram, the flue gases leaving the boiler must be in excess of 100°C in order that the flue gas does not condense inside the boiler or flue and corrode the boiler. Unfortunately, this means that a quantity of heat must be wasted in order for the boiler to operate at a high enough temperature to prevent this condensation.
Condensing boiler operation
Condensing boilers incorporate an additional heat exchanger to transfer latent heat from the flue gases to the cooler water entering the boiler, enabling them to produce around 10% more heat for every unit of gas used compared with a standard, non-condensing boiler. The heat exchangers used in condensing boilers are typically stainless steel to prevent the corrosive elements condensed out of the flue gas from harming the boiler.
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