How Does a Passive House Work?

Passive house relates to the way a building is heated:

Conventional buildings need active heating by means of burning oil, gas, wood or coal, or by electricity, either directly or indirectly by heat pumps.

Passive houses heat passively by means of energy conservation and by utilizing internal heat sources and solar gains.

The principle is like the comparison between a coffee machine and a thermos flask: both keep your coffee hot but one consumes energy and the other keeps the heat inside.

That's why a passive house has very well insulated shell and uses ventilation with heat recovery.