You can download the document for “An Introduction to Renewable Heating” here. Or view all documents available for downloads here.

Combis dispense with the need for a hot water cylinder and cold water cistern (and the smaller feeder cistern) as all the major components are housed in one unit, making then very convenient to the install as they take up very little space. The Combi unit houses a primary heat exchanger for the central heating system (heated by a gas or oil burner) and a secondary heat exchanger for the domestic hot water, which has a heat exchanger unit running from the primary heat exchanger unit. The mains water feeds into the Combi, inside which there is also a pump to increase the water pressure supplied to the house. The basic workings of a Combi are:


The advantages of this system are that:

  • They require little space

The disadvantages of the system are:

  • They are inefficient
  • They are expensive to run
  • They can’t be run alongside other systems (renewable)
  • They do not provide high pressure water
  • They are unsuitable for larger houses or those requiring a lot of heating
  • They require annual maintenance

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