This guide is intended to give a basic introduction to the subject of central heating boilers and flues.
The installation of central heating is a highly technical task and we strongly recommend the use of a fully accredited professional in ALL cases. Gas central heating is installed in over 70% of UK dwellings and has an excellent safey record, but there are inherent dangers associated with highly flammable materials and potentially toxic fumes which demand that installations are carried out by trained and experienced operatives.
We hope that this guide will help you to understand the various options that are available so that you can discuss with your chosen installer the system which is most appropriate to your needs. Further subjects will be featured in the near future and whilst every care has been taken in producing this section it should be noted that the information does not constitute recommendations and is simply a guide.
There are three traditional groups of boiler, Free Standing, Wall Mounted & Back Boilers. There are two other general categories, referred to as Condensing Boilers and Combination Boilers (usually referred to as Combis). All these types are described as follows.
Back boilers (BBUs)
One of the most significant effects of this is the 'pluming', sometimes mistaken for 'steam' coming out of the flue terminal. This effect is brought about by water droplets held in suspension in the flue products and although non-hazardous, it may be a nuisance if seen constantly passing across windows. This pluming will be evident for most of the time the boiler is operating, so care is needed in positioning the terminal.
Although they have a somewhat higher capital cost than non-condensing boilers, for larger dwellings (with three or more bedrooms) they usually prove to be cost effective within several years.
Typically, a condensing gas boiler might have a seasonal efficiency of around 88% compared to non-condensing boiler of about 75%, and an older type boiler at between 55% -60%. For more information, please visit www.boilers.org.uk website
They are as easy to install as any non-condensing boiler, but can only be fitted to 'fully pumped' systems. During it's operation, condensate forms and, although no more acidic than rain fall, a permanent pipe must be run to a drain
This type of boiler is available as a wall mounted or floor standing version.
In dwellings (often larger type) where a number of draw-off points (taps, showers etc) are likely to be used at the same time manufacturers advice should be sought as to the combi's suitability. Showers fitted to this boiler must be a 'mains pressure' type.
Because the boiler is fed directly with mains
cold water, it is vital to establish that the minimum water pressure,
specified by the manufacturer, is available otherwise the hot water
performance will suffer.
A combi (instantaneous condensing) boiler
operates in principle as an 'instantaneous' type but at somewhat higher
efficiencies (see condensing boilers above)
In general, the principle of operation is that the stored water will give up it's heat to provide an improved initial hot water delivery. Once the stored heat has been given up, the boiler then operates as an 'instantaneous' type.
A combi (storage condensing) boiler operates in principle as a 'storage' type but at somewhat higher efficiencies (See Condensing Boilers).
Combined Primary Storage Unit (CPSU) - This is a special category of storage combi and incorporate a very large store of water (usually more than 80 litres) allowing a high hot water flow rate to taps and other draw off points and quick heat-up to radiators.
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