Condensing Boiler

February 16, 2013 | Leave a Comment

What is a Condensing Boiler?

A Condensing Boiler, is the new generation of the Combination Boiler. It is also known as a High Efficiency Boiler. As technology has advanced, so has the design of the Combination Boiler. Evolving to the condensing boiler. This boiler is much more efficient than the original combination unit. This is due to the recycling effects of the new condensing boiler. When the condensing boiler was brought to the market it was around 75% efficient. As the manufactures strive to improve them, the current units are now up to 90% plus efficient Making them such a cost effective and space saving heating solution.

Condensing Boiler

Condensing Boiler

The efficiency of the condensing boiler, is due to the extraction of wasted heat. This heat comes from the exhaust and in the combination boiler was just vented out and lost. The condensing boiler has two combustion chambers. As apposed to one in the older combination boiler. This allows the boiler to gather back the heat about to be lost, reusing it and reducing the heat it needs to create.

The combination boilers have a single combustion chamber. This is enclosed by the waterways of the heat exchanger, the hot gasses pass over these waterways as they rise and flow out the flue which is at the top of the Boiler. These gases can leave the flue at over 180°c, making the boiler every inefficient and the flue pipe can be quite a hazard because of this. As water boils at 100°c it makes great sense to harness this energy and make use of it. It is this idea that gives the condensing boiler it’s second coil  through which the hot gasses eventually expel through the flue. Located at the top of the boiler, at a temperature around 180 degrees C.


What does a condensing boiler do?

The condensing boiler has been designed, to be  highly efficient. Giving it the other name of a “High Efficiency Boiler”.

It’s design firstly allows the heat, to pass through the primary heat exchanger. This is then through to the second heat exchanger. Their are some condensing boilers which are larger than the standard domestic unit. This will work off one number heat exchanger. But this has been designed to be more efficient.

Condensing boilers are able to reduce the exhaust gasses to around 55 degrees C. The reduction of heat from 180 degrees C to 55 degrees C causes the water to vapour. (This iso then formed during the combustion process) to condensate. The droplets of water as a result of the condensations, drop due to gravity. This then collects at the base of the flue manifold.

Condensing Boiler Diagram

Condensing Boiler Diagram

The remaining exhaust gasses are expelled through the flue to the environment. The condensing boiler design was brought about to:

  • A) Be more efficient.
  • B) Better for the environment.

The flue is fan assisted balance flue, as apposed to the straight flue of the Combi Boiler.

The condensed water is collected in a condensate trap, situated at the base of the condensing boiler. The trap has a syphoning array of pipework which allows the water to drain to foul. This can also go via a soak away. The reason for this, is the water is slightly acidic (about as strong as a fizzy drink). The pipework needs to be plastic as apposed to metal.  The reason that plastic is required is due to the acidic water will corrode the metal.


Condensing Boiler & Central Heating System.

For the condensing boiler to operate the central heating system & radiators. The domestic hot water-flow temperatures needs to be  between 75-80 degree C. Therefore the condensing boiler, although efficient, is not in condensing mode.

The condensing boiler only goes into the condensing mode, during the initial heat up.

The ability to achieve a central heating system which fully functions in a condensing mode. This is probably the next concept of condensing boiler. The installer needs to consider a suitable system of radiant heating to be more eco friendly.

N.B. Since April 2005 all Domestic Gas Boilers used in habitable dwellings a new High Efficiency /Condensing Boiler must be installed. Some exceptions do exist-please check with Local Authorities.



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