The key parts of a Passivhaus are:
Lots of it - in floors, walls and roof, without gaps.
Triple glazed in Britain, very wind - tight and carefully installed. A warm internal surface is provided, even in the coldest weather.
Ventilation with heat recovery
Continuous filtered fresh air, with pre-warmed incoming air.
Low air leakage construction
This eliminates draughts, and allows the heat recovery system to work efficiently.
Thermal bridge free construction
No cold spots that could lose heat and generate cold down-draughts.
Most heating comes from sunlight, occupants and appliances. On the coldest days a very small heating system is needed.