It’s perfectly possible to build a house that requires virtually no heating at all. If you insulate it well enough the heat emitted by people and appliances alone are enough to keep it warm. This isn’t new. Examples include the Whole Home, at the fantastic Centre for Alternative Technology (which you can visit), Hockerton Housing Project, or BedZed.
However, the UK housing stock isn’t generally quite up to that standard. The average family home faces heating bills of a thousand pounds a year. Typical heat losses are shown on the Before graphic.
The greenest thing you could do for most buildings usually doesn’t involve hi tech, expensive renewable technologies, impressive though they may look – it’s insulation, insulation and more insulation.