Passivhaus buildings work by ensuring that very little heat is lost through the fabric of the building, that is the floors, walls and roof. This is done by careful design and construction and ensuring that there are no breaks (thermal bridges) in the insulation layer which allow heat to escape and by making the building very airtight to stop drafts. They also use a heat recovery ventilation system, called MVHR (mechanical ventilation heat recovery), which ensures that you have plenty of fresh air all the time. The stale air that is being extracted has up to 90% of the heat passed back in to the incoming air meaning very little heat is lost. This allows the building to use the heat given off by the people in it and what they do to keep it warm. Because of this you have a reduction in your heating bill of upwards of 85%.
Compared to our last house I think we've reduced the heating bill in our passivhaus by around 95% using the Unger-Diffutherm wood fibre insulation systems in a timber framed house. Contact us if you'd like to know more.