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Know Your Boiler!
There are many factors to consider when choosing a new central heating boiler. This page offers guidance and advice to help you select the most suitable system for your home.

Boiler Types

There are broadly three main types of boiler:

Combination (Combi) Boilers

The combination (or 'combi') boiler is an increasingly popular choice in UK homes and now accounts for more than half of all new domestic boiler installations in Britain.

The principle difference between a combi and other types of boilers, is that a combi eliminates the need to store hot water (and therefore the need for a hot water cylinder in the airing cupboard). Combi boilers combine both a high-efficiency water heater and a central heating boiler in one compact unit, saving space and simplifying installation over conventional heating systems.

As well as saving space, Combi boilers offer significant saving on hot water costs as water is only heated as it is required. Other benefits include the fact that hot water is delivered through your taps or shower at mains pressure, providing powerful showering without the need for a pump.

Conventional (Regular) Boilers

Conventional boilers consist fundamentally of a burner that burns natural gas and produces flue gases. These flue gases are then passed through a heat exchanger, which extracts heat and transfers it to the water passing through the heat exchanger to provide heating and hot water.

If you are replacing an older model of boiler, it's likely that you will have a regular (conventional) boiler. A conventional system, typical incorporates a boiler with extended controls, a feed and expansion cistern, and a hot water cylinder (usually in an airing cupboard) which is often fed by a cold water storage cistern in the loft.

System Boilers

System boilers are compact, highly efficient and offer all the heating you need, with significant savings on running and installation costs.

A system boiler is a heat-only boiler that incorporates all the additional features required for a sealed, fully pumped heating system. This means installation is quick and easier than with some other types of boilers.

System boilers are generally larger then standard heat-only boilers due to the additional integrated components. They contain an expansion vessel with a pressure relief valve, gauge and filling loop as well as a pump. Conventional heating and hot water systems require separate, external feed and expansion cisterns and a circulating pump. With a system boiler these components are all built-in and ready to go, resulting in easier and tidier installation and the potential for greater reliability.

Boiler Efficiency

SEDBUK efficiency rating system for domestic gas and oil boilers

SEDBUK efficiency rating
system for domestic
gas and oil boilers
SEDBUK stands for Seasonal Efficiency of Domestic Boilers in the UK and is the Government sponsored energy efficiency rating system for domestic gas and oil boilers. It is designed to enable consumers to select appliances based upon their efficiency and is effectively an energy labelling system for heating appliances.

Since 2005, it has been mandatory in England and Wales through Building Regulations to only install 'High Efficiency' boilers, whether in new houses or as replacements.

A 'High Efficiency' condensing boiler is the most efficient boiler available. It converts more than 86% of the fuel it uses into heat, compared to 78% for conventional 'Standard Efficiency' boilers. There are two bands of High Efficiency boilers - SEDBUK A and SEDBUK B.

SEDBUK A High Efficiency condensing boilers use a primary heat exchanger to conserve the heat that would otherwise escape through the flue. This reduces the temperature of the flue gases to a point where water vapour produced during combustion is condensed out.

SEDBUK B boilers have a similar process but include a secondary heat exchanger.

Boiler Capacity

Boiler output is measured in KW or BTU/hr. When selecting a central heating boiler, you will need to consider your total heating and hot water requirements. There are various factors that will have a bearing on this, including: the number of radiators, sinks, baths and showers in your home, the size of your rooms, the level insulation etc. Our on-line quotation system is designed to help you ascertain your requirements.

This page is designed to provide general information only. Your choice of central heating boiler is an important decision and we recommend seeking the advice of an expert. Capital Heating's engineers are trained professionals and are always happy to offer unbiased help and guidance on the type and model of boiler. Please call us to discuss your requirements, on 01923 253629.