Boiler

We finally chose our replacement Central Heating boiler - the Alpha CD35 (http://www.alpha-boilers.com/). A number of local installers, including our chosen contractor, recommend the Alpha boilers and it has the advantage of being able to take a warm water feed into the domestic hot water system. This means it can potentially be linked in with a tank heated by solar panels, as in the following diagram stolen without permission from the Alpha website :

The text has been shrunk to the point of illegibility (you can find the original here) but the basic principle is that the solar panels heat a tank of water which is fed to a diverter valve that senses it's temperature. It is then routed either direct to the tap, or via the boiler for a "top up". The boiler is able to sense the temperature of the incoming water and modulate it's burner to suit.

Alpha also sell and "add on" to their CD range of boilers called the "GasSaver". This is a secondary heat exchanger that sits atop the boiler and uses heat in the flue gases to pre-heat the incoming cold water before it is fed to the boiler. Their claims for how good this is are very extravagant : "Fitting a GasSaver to an Alpha boiler could cut the amount of gas used to heat water by up to 52% a year". This sounds too good to be true, which, following the old adage, probably means that it is too good to be true !

In fact, I am struggling a little with the maths around this claim. According to the independent SEDBUK website, this is a category A boiler, hence boasts an efficiency of > 90%. Working on the assumption that this is a measure of how much of the calorific value of the gas ends up as heat in your water, then there is less than 10% disappearing up the flue that is recoverable by the GasSaver. A 52% saving is simply not there to be made.

The GasSaver unit is expensive (it nearly doubles the price of the boiler !), but if the savings claims are genuine it could be worth it. However we are not yet convinced.

Anybody got any views or opinions ?