What are condensing boilers?

Mr Peter Bellamy, Technical Director of Malvern boilers, explains the basic differences between traditional and modern high efficient condensing central heating boilers.

Malvern Boilers was set up in 1991 to produce a range of domestic gas condensing boilers. Since then it has established itself as one of the main forces in bringing the advantages of condensing products to the market, providing more than fifteen thousand Condensing Boilers into UK homes.

What are condensing boilers?

Condensing boilers are the most energy efficient Central Heating boilers on the market today. They achieve this high level of efficiency by removing the heat from the fuel it is burning and also cooling the products of combustion, which are normally wasted up the flue, so much so that the water vapour in them turns into liquid. This happens at around 55°C. For a boiler to cool the flue products this much, it has to have a larger, more efficient heat exchanger than traditional boilers.

So why aren't all manufactured boilers condensing?

• Well, firstly, because the liquid water, the condensate, has to be safely removed from the boiler and to include this into the design requires the use of materials not normally used in traditional boilers.
• Secondly, the natural buoyancy of the flues products is lost when the temperature is brought this low so it is necessary to have a fan to remove them.
• Finally, larger heat exchangers cost more to make so the boilers will be higher in price and it takes very clever designs to ensure that the user will be able to save more in reduced fuel bills than they spend on the extra cost of Condensing Boiler.

The design that Malvern Boilers use does just that. We have split the heat exchanger into two parts and used an ordinary non-condensing copper heat exchanger for the first, and a patented aluminium design for the second. Aluminium is one of the materials that can be used in the condensing section but it is not so good on the system water side. Consequently we line the second heat exchanger with copper. This way the system sees nothing but copper in a Malvern Condensing Boiler.

There is also another benefit obtained by the water vapour turning into liquid, it gives up energy, which is called latent heat. This adds to the rest to make the overall efficiency of a condensing boiler maybe 15% greater than a modern non-condensing one. The more efficient the boiler is, the less fuel it uses, the less carbon dioxide it produces and the less it costs to run.

Comparative efficiencies and running costs will be examined in more detail in another article.

Are they expensive?

They cost a little more, for the reasons already mentioned but this should be paid back in perhaps as quickly as two years.

Aren't they more complex and difficult to service?

All Malvern Condensing Boilers have been made using industry standard parts and are no more complex than a modern powered flue boiler.

Are there special installation requirements?

They do need one additional installation requirement, a pipe to drain away the condensate. This can be into any of the existing waste water outlets in the property or even into its own mini soakaway, more of this in a later article.

No, the standard radiator sizes will be just fine. This will also be explored in more depth in a future article.

Do you need complicated system controls?

The minimum standard for any domestic installation is a Room Thermostat, an Electric valve, and if a hot water cylinder is needed, a cylinder thermostat. This will be fine for a condensing boiler too. You can also have Thermostatic Radiator Thermostats (TRV's), but if they are on every radiator a bypass must be fitted.