What is a ‘Combi’ Boiler and which one should I buy?

A ‘combi’, or combination, boiler is so called because it is a combination of a central heating boiler and instantaneous water heater in one cabinet (usually it is necessary to do away with separate cold water tanks and hot water cylinders, saving a lot of space).

Combis deliver the hot water at mains pressure, which is excellent for showers, but it is very important to ensure that you choose a boiler which will deliver enough hot water for your normal needs – the more powerful the boiler, the more water it can heat in a given time. Both Gas and Oil fired combination boilers are readily available and offer a range of features to suit many homes.

All combis are NOT the same - we would advise using boilers made by well known British or European manufacturers that have good track record of reliability and spares / service backup in this country. We will be happy to suggest suitable models for your needs.

Can I still have an ordinary boiler?

Yes! It is still possible to have a conventional floor-standing or wall-mounted ‘heat-only’ boiler fitted. Some installers may find it easier to fit combis and suggest – incorrectly – that other types of boiler can no longer be fitted.  There is still a place for this type of boiler and they will continue to be available from major manufacturers.  When fitted with suitable up-to-date controls, a condensing conventional boiler should have a very similar energy efficiency to a condensing combi boiler.

What is a ‘Condensing’ Boiler?

A ‘Condensing’ or ‘High Efficiency’ boiler is designed to extract about 15% more heat from the fuel burned that a ‘Standard Efficiency’ boiler – it does this by having a heat exchanger which cools the burned gasses to a much lower temperature, thus extracting more heat from them. A large part of the ‘products of combustion’, produced when fossil fuels such as gas and oil are burned, is made up of water vapour. In a standard boiler this is sent out in vapour form at a temperature well above boiling point, however, a condensing boiler cools the gasses down well below boiling point and most of the water condenses out inside the boiler – hence the name. A special Condensate Drain is needed to remove this liquid from the boiler to a suitable drainage point.  Some of the condensed vapour is carried out through the boiler flue and is seen as a ‘plume’ of steam-like appearance, especially noticeable in colder weather.

New Building Regulations, which came into force in 2005, mean that almost all new or replacement gas boilers will need to be ‘condensing’ types in order to satisfy the requirements for minimum boiler efficiency.  Oil fired boilers for domestic heating installations are now subject to similar regulations.

Can I still have a New Back Boiler Unit?

Possibly!  No brand-new back boiler installations are permitted (i.e. where a back boiler is not already fitted), BUT, it is still possible to buy back boiler units with fitted gas fire-fronts.  Part L of the Building Regulations requires installers to ensure that it is not realistic to install a condensing boiler without causing major disruption to the house before considering replacing an existing back boiler with a new one.  There is a good reason for this, Back Boilers are much less efficient than current condensing boilers – typically being in Efficiency Band D or E as compared to Bands A & B for condensing boilers.  Whilst they are convenient and space saving, the low efficiency and the fact that they are large ‘open-flued’ appliances (with the attendant safety concerns) means that back boilers are better avoided if at all possible.