Modern Condensing boilers, the underlying truth can make interesting reading. Whilst the boiler gently on this, or doesn’t, in the corner of the utility room and constantly provide hot water to your home you may not be aware but a very clever design has resulted in a very efficient machine, a thoroughbred in the world of energy efficiency.

A condensing boiler is a high efficiency forward-looking boiler that incorporates an additional heat exchanger in order that the red-hot flue gases transfer much of their energy to start to heat the cold water input. When working at a good efficiency, the water gases developed in the running action turns revert back into clear water releasing the latent heat of vaporisation. In layman’s terms this means that a condensing boiler is miserly and doesn’t want to let any waste heat disappear outside. In fact it cleverly uses the heat that hasn’t been used to heat water to actually heat new water which is entering the boiler. Two bites at the cherry here to ensure that you get the maximum bang for your buck as they say.

A side effect results in this liquid, called condensate, typically acidic, should be piped outside to a drain or soakaway. The boiler will be fixed against a wall and the exhaust gases will pass through the flue. Hot water is served by a small-scale recepticle tank to ensure convenient and rapid hot water availability.

What size of boiler should I get?

It was a earlier practice to install outsize boilers. Whilst this meant that there was no possibility of the boiler being unable to supply sufficient hot water, without any care for icy weather, it also meant that they were mainly running at a part load, and so working under their designed optimum efficiency. If you have installed further loft or cavity wall insulation since the last boiler was fitted, it could well be that you will be urged to install a smaller boiler than before.

Before you purchase a new boiler we advocate you get advice from a registered fitter, there are too many choices for you to stick a pin into a booklet and select a boiler that looks nice. You need one that is on the right design and right size to fit your house and deliver the heating that you need and the hot water when you want it.

Do the radiators need to be outsized with a condensing boiler?

The underlying reason for this improved efficiency from a condensing boiler comes from having a larger heat exchanger. Larger radiators would result in cooler return water temperatures, and so enable greater energy efficiency, but the further savings suffer from falling returns, bearing in mind that the system is working at very low capacity for the majority of the heating season. That probably remains true, though the smaller heating requirement for new build may well mean that householders would now endure over-sized radiators more willingly.

The SEDBUK project looked at this, and had a look at the recommendations for condensing boilers. The determination was that they need not, and the test results forthe condensing and the existing boilers employ the same SEDBUK formula.

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