Any combi will provide an adequate amount of heat for a two bedroom house (the smallest output on the market is 24kW and an average two bedroom house would only require about 14kW).
The hot water production is the main difference between boiler sizes, and a 24kW boiler will only provide adequate hot water. The difference in cost between a 24kW, 28kW, and a 32kW combi will be about £100.00. If your budget will stretch to a larger output boiler, you will see the benefits in hot water production.
Whichever size boiler you choose, bear the following in mind;
1] It MUST be installed by a CORGI registered installer.
2] It MUST have a SEDBUK rating of at least B, but prefferebly A (SEDBUK is the energy efficiency rating)
3] The boiler MUST be installed in compliance with Part L of the Building Regulations.
4] If the boiler is to be installed in the garage it MUST be a room sealed appliance
5] Installion in the garage will mean that the electrical wiring to the boiler MUST be compliant with Part P of the Building Regulations (a qualified electrician holding the current test and inspection certificates will be required)
6] The heating load must be range rated to suit the house (the amount of output to the central heating can be adjusted to ensure the boiler is not wasting gas by producing more heat than the radiators require when running the central heating )
For a CORGI registered installer in your area contact CORGI on 0870 401 2300 or follow this link http://www.trustcorgi.com/findinstaller/findinstallerlanding.htmx
David Hickey
January 2007