The idea is to keep the heat inside, not the air. Passive houses typically come with special ventilation systems that completely exchange the air once every 2-3 hours, while keeping >80% of the energy inside. This kind of design is becoming increasingly popular here in Germany.
Cool. I asked because there have been some problems with energy efficient houses in the Netherlands. People actually got health problems because the ventilation doesn't work well enough. Have there been independent studies of air quality for the houses in Germany?
I don't really know, and I don't speak from first-hand experience. But from what I've heard, the main concern is not air quality, but humidity. When you heat up air, its relative humidity goes down. So especially in winter, the ventilation system can blow very dry air into the building. There are simple technical solutions that artificially "humidify" the air, but it's definitely something to look out for. Low humidity can cause all sorts of health problems.
