Ventilation in modern homes seems like it may be unnecessary for a green building and/or home when cracking the windows seems like the best and cheapest option. However modern homes have far more volatile organic compounds, formaldehyde, flame retardants and
other chemicals that can give off significant off-gassing as discussed in this article.
100 years ago, homes were made with mostly natural products. They were also quite leaky, they also did not have insulation in the walls. This allowed air to come in and out of the building through the gaps and cracks and holes in the building envelope.
There are many different ventilation options and they can take many different forms. Generally speaking, there are around six generic types of ventilation systems:
1) No Ventilation. This is by far the most common option in homes in America. This strategy used to work when houses weren’t sealed as tightly as they are today. Getting air from inside out and vise-versa can prove difficult on non-breezy, stagnant days. Especially in the summer and spring when fresh air is most desired.
2)Natural Ventilation. This is not a common strategy. It uses a solar chimney where air is heated by the sun, becomes more buoyant and exits through the chimney. There are also strategically placed inlet ports where fresh air can enter.
3) Exhaust-only mechanical ventilation. Relatively common. Small exhaust fans, usually in bathrooms, operate continuously or intermittently to exhaust moisture and stale air generated in those rooms. This system creates a modest negative pressure in the house that draws fresh air in from outside.
4) Supply-only mechanical ventilation. A fan brings in fresh air and the stale air exits through cracks and air leakage sites in the house. A supply-only system pressurizes a house which can help to keep out radon, a contaminant, from entering the house. The only issue with this system is that it can force moist air into ceiling and wall cavities where moisture problems can occur.
5) Balanced Ventilation. Better ventilation system with separate fans that drive inlet and exhaust airflow. This system lets you choose where fresh air comes in and where stale air exits. You can choose to deliver fresh air to more lived-in rooms and release air in more moist and polluted rooms of the house.
6) Balanced ventilation with heat recovery. If you have separate fans for fresh indoor air and exhaust indoor air, keeping these fans close together allows for a air-to-air heat exchanger to be used so the outgoing house air will precondition the incoming outdoor air. It keeps the air in the household to desired humidity in the winter and reduces the amount of humidity introduced from the outdoors in the summer.
For the best air quality in your home, a mechanical ventilation system is highly recommended. Although mechanical ventilation uses energy, having the heat recovery system keeps the penalty of using energy for fresh air minimal.