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How Do Condensing Boilers Make Water Hot?

This article will look at the parts within a condensing boiler, how they differ from conventional boilers and what water does when it flows through them.

The heating process is started by a part at the bottom of the boiler called the burner. The burner is fitted with a small nozzle that atomises the oil, much like putting your finger over the end of a hose. There are two electrodes that light the oil, generating heat which travels into the combustion chamber and on into the primary heat exchanger.

The primary heat exchanger is located just above the burner. This contains a group of ‘baffles’ which is essentially a group of interconnecting metal chambers that forces the hot air to travel up through them before being released into the condensing chamber. The reason for the complex maze of baffles is to keep the hot air within the primary heat exchanger for as long a period as possible, giving the water the best possible chance of collecting all the heat.

Finally, above the primary heat exchanger is the condensing chamber, which contains a series of downwards-sloping cylindrical holes. Each cylindrical hole contains a spiral fin that collects any water droplets collected from the rising heat and disposes of them safely via the run-off drain.

To compare how a condensing boiler is different (and more efficient) than a conventional one, we will first look at how water flows through a conventional boiler.

With a conventional boiler, there is a heat input of 300°C at the bottom with a standard set of baffles above it. The return pipe, containing the water being returned from the heating system, enters at the bottom and travels through the boiler picking up heat before exiting back into the heating system through the flow. The main problem with this type of boiler is that the heating process causes a huge amount of heat energy (up to 250°C) to be lost out into the atmosphere via the flue.

With a condensing boiler, there is again a heat input of 300°C at the bottom, but it contains a more modern and technologically advanced double column of baffles, plus it contains the condensing chamber on top. The biggest difference between the boilers is that, in the case of a condensing boiler, the return pipe enters the condensing chamber first, allowing the water to pick up latent heat. After flowing through the condensing chamber, the return pipe then flows into the bottom of the boiler and through the primary heat exchanger. The water takes on all this heat and flows back out into the heating system. Whereas with a conventional boiler, the heat lost via the flue was 250°C, the heat lost from a condensing boiler is only around 55°C. This is because so much more heat has been extracted and put into the water, making the condensing boiler a much more efficient way of heating water.

Article by Benjamin Clarke