What’s the difference between having a combi or condensing boiler?

When it comes to boilers most of us have heard of both terms but understanding what they really mean can often leave people scratching their heads. Luckily, the answer is simpler than you may think. Below is a clear explanation that helps solve the mystery of, ‘do I need a combi or condensing boiler’?

The main thing to understand is that the term ‘condensing’ refers to the way a boiler functions; which is to say that it captures heat from waste flue gases – which would otherwise be released into the atmosphere – and recycles it back into your heating system. And it is this high efficiency technology that you will find in all modern combi boilers (as well as in conventional or system boilers). In fact, the law now mandates that all new boilers for domestic homes* must be condensing boilers (also known as high efficiency boilers). Non-condensing boilers are no longer allowed to be installed.

Compared to a non-condensing unit, gas condensing boilers use less fuel and power. This is thanks to heat exchangers inside the boiler which, during the heat recovery process, rapidly cool the waste gases and ‘condense’ the water vapour into droplets (or condensate), which is what gives the boiler its name. This means that a condensing combi boiler can convert over 90% of the fuel it uses into heat. Such combi boiler efficiency, together with reduced waste CO2 emissions, ensure you can enjoy economical and environmental benefits respectively.

We hope this information gives you the confidence to seek out new combi boiler deals safe in the knowledge that they will all be condensing. A Gas Safe registered engineer will be able to conduct a home survey and help you choose the best size combi model to suit your property and hot water demand.

For further peace of mind, all gas condensing boilers are covered by ErP regulations. Standing for ‘Energy-related Products’, a boiler ErP rating that tells you that an ErP combi boiler is 92% efficient (which is shown as ‘A-rated’ on the ErP label).


*In this context we are referring to domestic homes connected to the mains gas network and hence requiring a gas condensing boiler.

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