Condensing Boilers – Old Hat Now!

To say you have one of those new fangled condensing boilers in your house, is a bit like saying you have an engine in your car.

Condensing boilers represent great technology, but it’s almost a universal technology now in the UK, and indeed most of mainland Europe, because it’s the only way that boilers can reach the required levels of efficiency demanded by the latest building regulations.

These now state that boilers which cannot achieve 90%, or more levels of efficiency, cannot be used in new builds, or refurbishments. There are of course exceptions, but this only happens when the siting of a boiler (say in a listed property which can’t site a boiler anywhere else) cannot accommodate the extra pipework and controls. And the process of condensing means that these high efficiencies can be reached.

In theory, condensing boilers use a technique of heat capture which is quite simple and easy to understand. A boiler which does not use condensing technology, has effectively one grab at the heat provided by the fuel; at the time of combustion. Everyone knows that a large proportion of the heat combusted is lost through the chimney, or flue. In most cases, some 40% to 50% of the heat from the combustion process can be lost like this.

Which is why back boilers heated by open fires were so inefficient and frustrating for householders.

Now, if you could harness that waste heat, naturally you would be more efficient. So, condensing technology does just that: it grabs the heat produced by the combustion process – contained in the waste gases – and uses it to also heat the water. This means that modern boilers will use over 90% of the original heat combusted to heat the water and only a very small amount of heat will escape up the flue.

Great. The only downsides are increased cost of parts and installation. A condensing boiler requires more bits: it needs two aluminium heat exchangers (one for the original combustion process and one for the exhaust gases); it needs a drainage pipe to take away a liquid which is formed from the rapidly cooling exhaust gases (called condensate); and, it needs a fan in the flue to ensure that the colder exhaust gases are pushed out into the atmosphere, rather than dropping back down the flue.

Thus, greater efficiency levels, but an increase in costs. And the siting of a boiler becomes ever more important, because the drainage pipework needs access to an outside wall and drain.

And, of course, another issue which cropped up the winter before last when temperatures dropped to record lows for long periods of time. Condensate is basically water and freezes; thus drainage pipes quickly froze and shut down the boilers. Therefore, condensing boilers need proper controls to prevent that from happening.

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