How much CO2 can I save?

Well, here's the answer from all properties in the Carbon Census to date :

On average a UK household can save 2 - 6 tonnes of CO2 each year by implementing all of the measures identified in an official Energy Performance Certificate. About a third of the saving can be achieved with relatively cost effective measures - lighting, insulation, thermostats, heating system and so on - and about two thirds from more expensive improvements such as installing solar thermal hot water, solar panels or solid wall insulation. That said, solar panels are one of the more cost effective investments now that feed-in tariffs have been introduced. A typical installation saves about 1 tonne of CO2 per household per year.