Condensing boilers, a brief guidebook

A condensing boiler is a finance saving innovative boiler that contains an additional heat exchanger in order that the hot exhaust gases transfer most of their energy to pre warm the water in the boiler system. When operating at high efficiency, the water vapour developed in the burning action distils back into a liquid relinquishing the latent heat of vaporisation.

A fallout will be this water, named condensate, that is frequently acidic, will need to be piped outside to a waste pipe or water drain. The boiler should be mounted to a wall and the exhaust gases will travel through the flue. Hot water is initialy served by a modest recepticle tank to enable quick hot water availability.

Can you advise on the right boiler size?

It was a past practice to install oversized boilers. Although this ensured that there was little chance of the boiler falling short on its requirements, without any concern for icy weather, it also meant that they were principally working at a reduced capacity, and so working under their designed optimum efficiency. If you have fitted additional loft or cavity wall insulating material since the current boiler was fitted in your house, it is highly likely that you will be able to fit a lower capacity boiler than before.

Before you get a new boiler we advocate you get advice from a CORGI registered installer.

If I fit a condensing boiler should I fit large radiators?

The main efficiency benefit from a condensing boiler is that it has an oversized heat exchanger. Bigger radiators would allow lower return temperatures, and so result in even better energy performance, but the additional saving is not shown to be cost effective, keeping in mind that the system is running at very low capacity for the majority of the heating season. Whilst this assertion is correct householders would plausibly accept this in smaller properties.

The process we have discussed was incorporated in the terms of reference for the SEDBUK project, and had a look at the recommendations for condensing boilers. The determination was that they need not, and the test results for both types share the same SEDBUK computation.