Combi boilers

Summary: Combination boiler guide, advantages of a combination boiler and disadvantages of a combination boiler.

Combination boilers

A combination boiler or combi-boiler is a particular type of condensing boiler. They are the most popular type of system as they combine the ability to heat the domestic hot water (DHW), which is the hot tap water system and central heating from the same location. When DHW is run, the boiler stops pumping water to the central heating circuit and diverts all the boilers power to instantly heating the DHW. Because it gives priority to the DHW, instant heated water is still provided in the same way it would if it had its own system.

Heat is made when the refrigerant in a cold liquid state is sent through the coiled pipes from inside to outside. The outside air passing over the coils causes the liquid refrigerant to heat up and boil, turning it into a vapour. The vapour is condensed creating greater temperature to be used in heating the required aspects of the building.

Advantages:

  • Combi boilers have fewer components, making them simpler and also less greedy in terms of space usage. The more traditional central heating systems store the pre heated water in a cylinder in the airing cupboard. This water provides the DHW. Combi boilers do not require this cylinder which will save you space and will reduce the energy wasted through heat loss, making them more efficient than most boilers.
  • The conventional cold water storage tank (usually located in the loft) is also not required if you have a combi boiler system. As combi boilers do not store water, the cold water is instead fed straight from the mains supply, which is heated up as you use it.

Disadvantages:

  • The only recognisable disadvantage to having a combi boiler is the possibility of low hot water pressure. Although there is a constant flow of hot water available for the user, the flow rate can be reduced because of the need to heat the water, which does not exist with the pre-heated water found in older systems. Heating water when needed is an advantage of the combi boiler but can limit the volume available at any one time – particularly in winter.
  • Due to the fact that the boiler is fed straight from the mains water supply, it is important to check that the water pressure of the mains is satisfactory for the combi boiler to perform adequately. For this reason, in areas where the pressure may not be high enough, a combi boiler would not be suitable.

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