A passive house needs to constantly circulate air in order to maintain its internal air temperature and quality. A passive house pulls air from outside and passing it through pipes, buried below ground, with the use of a mechanical ventilation system, such as a heat recovery (HRV) or energy recovery ventilator (ERV); in the winter, air is preheated and in the summer, air is precooled.
Air inside a passive house also passes through the recovery ventilator. This air exchange process, which is minimal, maintains a comfortable air temperature all year long. Because a passive house is essentially a sealed, air tight building; heat from people, pets, appliances and sunlight can impact its internal temperature during the winter months; in most cases, eliminating the need of an additional electrical heating source.
So, what happens when you lose electricity?
In the summer, open your windows; what do you do in your house?
In the winter, light a candle! That's right, its been proven that the heat output from up to 20 candles, in an average size passive house, can provide enough warmth to stay toasty during the winter.
The video clip below offers an animated explanation of a passive house's mechanical ventilation system.