When thinking about the best HVAC system for a residence or building, you should consider energy efficiency and building size. Choosing an energy-efficient system will not only help to keep monthly energy costs down, but it will also reduce environmental pollution associated with electricity use. The size of the home or building is also essential because it helps determine what type of unit should be installed and how powerful it needs to be so that it can efficiently heat/cool the entire structure. Each HVAC system has advantages depending on usage requirements and climate conditions, such as temperature range in different seasons during a year in a given location; humidity level; average wind speed; etc. Consult with an expert contractor specializing in this field to determine the best type.