A Brief Guide to Condensing A Gas Central Heating Boiler and Hot Water Heater

A Brief Guide to Condensing A Gas Central Heating Boiler and Hot Water Heater
Written by Alyssia Walmsley

Most boilers installed in British homes are condensing combination boilers, known as combis.

Domestic Heating & Hot Water

A combi is a water heat and a central heating boiler combined. It does not produced stored hot water, it produces continuous, unlimited hot water on demand, it fires up every time a hot tap is turned on. It is, therefore, different to a traditional wall hung or floor standing boiler which is a central heating boiler with a secondary role to heat up water which is stored in a separate cylinder.

This type of system is generally cheaper than traditional or regular central heating systems because there are less parts to the system, it is simpler. Cheaper, however, does not mean inferior. There are many advantages to having a combi but they are not perfect for every domestic situation.

Condensing Combi Boilers

Almost all new U.K. boilers condensing regardless of whether they are combis or traditional, regular boilers, which are sometimes called “heat only boilers”. This is to comply with the U.K. Building Regulations’ requirements for High Efficiency boilers in order to reduce carbon emissions. These regulations apply to new build houses and old, existing buildings.

Benefits of a Combi Gas Heating Installation

  • Generally cheaper than regular system to install;
  • Constant hot water;
  • Hot water at mains pressure provides a powerful shower without a pump;
  • Not heating and storing hot water which may not be used.

Disadvantages of Combi Central Heating

There have been two main complaints about these boilers:

Firstly, the flow of hot water may be disappointing, especially in cold weather because the boiler is heating up directly as water enters the house from the cold water mains.

Secondly, the boiler is not suitable for multiple users drawing on water. There is one lot of mains water so if two hot taps or two showers are turned on the supply of water to each will drop.

There are a large number of single person households, in addition many couples and even families who will not be troubled by these disadvantages. homes in which there is only one bathroom and for whom this would not be a problem. Again, a high rate of litres per minute will help to militate against this problem.

Combination Boilers & Domestic Hot Water Supply

Manufacturers have risen to the challenge to over come perceived combi problems. There are different boiler specifications and for this you need to compare the output of litres per minute given a particular rise in water temperature.

16 litres per minutes is very good some models claim to produce 20 or 25 litres. Some models of combi also store hot water and use the stored water to increase the litres per minute flow rate and support several bathrooms.

Examples of these boilers include:

  • Worcester-Bosch Greenstar Highflow A range of floor standing combis which can deliver up to 20 or 25 litres per minute given a mains water pressure of 1.7 bar. They claim it is suitable for large houses with up to 3 bathrooms.
  • Vaillant ecoTEC plus 937 power store A combi boiler which stores hot water for properties with high water demands.

How to Choose a Combi Boiler

A new boiler must be installed by a registered, competent gas heating engineer. This person will be able to advise on selecting the right boiler

About the author

Alyssia Walmsley

Alyssia is a Cornell University graduate of 2003 and a former lead technology development manager for Microsoft and Cisco Networking Systems. Between writing on her blog, Blubbr, she likes adventures and chocolate sprinkles.

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