how does a heat exchanger work in a boiler

A heat exchanger in a boiler transfers heat from the combustion gases to the water circulating in the system. Here's how it works step by step:

1. Combustion occurs: The boiler burns a fuel source (like natural gas, oil, or electricity), creating hot combustion gases.

2. Heat transfer to the heat exchanger: These hot gases flow through a heat exchanger—typically a coiled or finned metal tube or series of plates made of steel, copper, or aluminum.

3. Water circulation: Cold water from the central heating system is pumped through the heat exchanger.

4. Heat absorption: As the hot gases pass over the surfaces of the heat exchanger, heat is conducted through the metal into the water inside.

5. Hot water delivery: The now-heated water is circulated through radiators or to hot water taps, depending on the boiler type (combi or system boiler).

6. Gas expulsion: The cooled combustion gases are vented out through a flue.

In condensing boilers, there's an extra stage:

• After the initial heat transfer, the remaining heat in the exhaust gases is used to preheat incoming cold water, extracting even more energy and improving efficiency. This process often creates condensate (water), which is drained from the boiler.