So, with the new energy code looming, that basically makes new homes and major renovations more air tight than ever, people are asking us if houses need to breathe. The answer is yes, and it is more important now than ever. Houses need a mechanism in place to allow warm moist air to move out of the house in a controlled and predicatable fashion. There are only two ways to do that, first is to have bath fans run continously when people are in the house. The second is with a heat recovery ventilator, that brings fresh air into a house, and evacuates air at a set rate. Our experience has been that the heat recovery ventilator, although more expensive than the bath fan solution, is a much better way of controlling fresh air exchange in a home.
Here is an article on the subject from housingzone.com : http://www.housingzone.com/green-energy-efficiency/building-science-do-houses-need-breathe