Condensing Boilers they say are the most efficient fuel burning Central Heating System boilers in a building. The efficiencies typically may run as high as 98 % according to claims by the manufacturers. The same items on test beds of units of certifications according to SEDBUK of UK on the other hand would show this to be around 95 % at best. In real life this can be typically about 82 % - 89% and would be about 90% at best. Bear in mind that all these efficiencies are worked out when High Heating Value (HHV) fuels are used and conditions are near ideal.

Conventional Boilers have efficiencies ranging from 70 % to 80% and no more. So still one could say the condensing boiler is more energy efficient. But it boils down to whether it is a worthwhile investment when you want to replace your old conventional boiler or buy a new boiler for your new house.

To really understand how this disparity occur one must understand the working of a condensing boiler.

Working of a Condensing Boiler

The condensing boiler too is a fuel burning device which utilizes the intrinsic energy of the burning fuel (generally some form of fossil fuels) to elevate the temperature of water circulating in a heat exchanger up to boiling condition or superheat. Typically this much is common for both types of condensers. In both cases the flue gases are exhausted. The condensing boiler deviates here in that, the steam or vaporized water in the flue is made to give up its imbibed thermal energy (called Latent Heat of vaporization) back to the system by means of a secondary heat exchanger. This waste heat recovery is what makes the condensing boiler hover around 98% efficiency (on test bed that is).

How to overcome the low efficiency?

In order to even achieve this level of performance, there are several conditions to be maintained. For e.g.

•The return water temperature from the system has to be low as possible for the maximum water vapour to condense releasing the latent heat and elevating the total heat generated. A flow temperature of 50 0 C would be good temperature for this.

•On the other hand when the return water temperature is that low the hot water takes quite a longer time to heat up to the useful temperature which is about 84 0C. (The longer heat up duration is not an acceptable situation to the ultimate user).

•All condensing boilers are delivered from the factory with a default setting which is high and set that way in order to provide the system the widest practical in /out temperature difference. However this disregards the need for the high fuel efficiency which is the prime the requirement in preferring the condensing boiler (over the conventional boiler) in the first place.

•Combining the domestic hot water and space heating systems to the same boiler would improve the seasonal energy efficiency. This arrangement however might need a duel temperature valve having settings of 63 0C (fully condensing condition) and 84 0C (partial or zero condensing).

In any event the condensing boiler still maintains higher fuel efficiency than the conventional boiler though this would not make you eligible for any grants and high green BER ratings.