Ventilation systems in green homes can vary from the standard heating, ventilating and air conditioning (HVAC) systems in more traditional homes. There are green HVAC systems, but separating the air conditioning and relying on the mechanics of moving air is one way that a green home can violate standard building codes.
Often large air conditioning units and furnaces do the work of removing hot air from rooms and keeping hot air in rooms, depending on the seasonal needs. Many HVAC units are ENERGY STAR approved and are already code-compliant for efficiency. Green mechanical systems, however, regulate temperature and moisture within rooms, but they do so by utilizing outside air and air circulation rather than air conditioning, which relies heavily on electricity.
If working properly, these mechanics operate well and natural outdoor air flows, producing healthy and comfortable indoor conditions. Making them compliant with codes for indoor air quality might be a bit tricky, though, because unlike traditional HVAC units, requirements for outputs or inputs of natural air and heat based on square footage aren't widely recorded in codebooks, yet.