Choosing your High Efficiency Condensing Boiler

Free standing floor mounted boiler

These floor standing boilers are usually fairly 'slim' for fitting between kitchen units, although they may be installed in any suitable location. They are available as Room Sealed, Fanned Flue or Conventional open flue versions.

Wall mounted boiler

The vast majority of boilers these days are wall mounted. These boilers have lighter, more compact heat exchangers, constructed from materials such as copper, aluminium, stainless steel or lightweight cast iron. They are available as Room Sealed, or Fanned Flue versions. The Conventional balanced and open Flue version of this boiler is no longer available.

Most modern boilers of this type, are required to have a 'system by-pass' fitted to allow enough water to circulate through the appliance to prevent 'kettling' (the same kind of noise associated with a 'singing' kettle) and to protect the motorised valve



Back boilers (BBUs)

Under recent building regulations, an old back boiler in the fireplace area should be replaced by a condensing or high efficiency boiler. Back boilers are known as open flue models, which should, in most cases, no longer be sold. The only exception is when it is either too complicated or expensive to install a condensing boiler. In that case a back boiler can be fitted providing it achieves a minimum 78% SEDBUK efficiency. SEDBUK stands for Seasonal Efficiency of Domestic Boilers in the UK. Many customers faced with this, tend to opt for a new condensing combination boiler which frees up the fireplace to put in a more attractive gas fire, or simply leave it open.

Condensing boilers

Condensing boilers have been around for many years and users report very significant reductions in fuel costs in some cases. This is possible, because this type of boiler has a much more effective 'heat exchanger' allowing more heat to be removed from what goes up the flue. 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 not dangerous, 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 think carefully about where you put it. Although they can be initially more expensive than non-condensing boilers, for homes 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 at about 75%, and an older type boiler at 55%-60%. They are as easy to install as any non-condensing boiler, but can only be fitted to 'fully pumped' systems. During its operation, condensation forms and, although no more acidic than rain fall, a permanent pipe must be run to a drain Condensing boilers can be wall mounted or floor standing.

What is the cheapest boiler?

According to the Energy Savings Trust there are approx 2270 types/models of boiler available on the UK market. High Efficiency Condensing Boilers can be purchased for under 350; however YOU PAY FOR WHAT YOU GET. If the 350 boiler was as good as a boiler double the price (ie 24kw Saunier Duval combination boiler 400 verses equivalent 24kw Worcester Bosch 600) we would all buy the cheaper boilers We recommend that before you invest in a new boiler - you seek advice from a person that repairs boilers as they can advise the faults and reliability. A well known German manufacturer recently launched a boiler that kept catching fire as they had developed the wrong seals - these boilers are still out there in the market place (ps - we will not install any of this manufacturers boilers as we do not want a call from a customer informing us that there house is on fire)

• Fab Fab boilers - (based on reliability and efficiency):
  Worcester Bosch, Viessmann, Selected models from Potterton, Buderus
• Bad Bad boilers - too many to mention

Combination Boilers

Combination boilers are by far the most popular boiler type, accounting for over half of all new boiler sales within the UK. Most wet central heating systems use a boiler to heat a copper cylinder in the airing cupboard to provide hot water. A combination boiler (usually referred to as a 'combi') heats water for the taps from within the unit and combines this with central heating. Combi boilers don't need a water cylinder on a cold water tank to feed it. Hot water running costs are therefore slightly lower. The water is heated as you use it and doesn't sit in a cylinder which is gradually going cold. However, the rate at which hot water comes out of the taps is not likely to be as good as with a traditional storage cylinder, particularly in Winter.


Combination boiler

In homes where a number of taps and showers are likely to be used at the same time, you should seek manufacturers' advice on whether or not the combi is suitable. Showers fitted to this boiler must be a 'mains pressure' type. Because combi boilers are fed directly with mains cold water, there must be enough water pressure for them to work properly. Manufacturers will state what the minimum pressure should be for each model. If you have low pressure there are options to improve the flow rate and water pressure, please call our office to discuss these solutions - 0208 492 0077 (9am - 5pm)

Types of combi boilers

A combi (instantaneous) boiler is the most widely used type and directly heats incoming mains cold water to supply hot water to taps and showers.



A combi (instantaneous condensing) boiler operates in principle as an 'instantaneous' type but at somewhat higher efficiencies (see condensing boilers above)
A combi (storage) boiler is a variant of the Instantaneous type and is designed to give better hot water performance. Dependent upon the make and model, the improvement in hot water delivery will depend upon the size of hot water store, and this can vary considerably.



The stored water will provide an improved initial hot water delivery and once this has been used the boiler then operates as an 'instantaneous' type. A combi (storage condensing) boiler operates in principle as a 'storage' type but is more efficient. Combined Primary Storage Unit (CPSU) - This is a special category of storage combi and incorporates a very large store of water (usually more than 80 litres) which creates a high hot water flow rate to taps and showers and heats up radiators quickly.