The best HVAC system in our house is no system at all. Wood heat, via stand alone wood stove, and two small window air units, provide the perfect heating and cooling system here. Two story, with windows facing south, and enough overhang from the soffit to provide shading in the summer, good sealing and insulation, living areas where there is radiant heat. The "HVAC" system here over the last decade has seen little use, and is used as backup only. We're very comfortable -40f to 100f. 2500sqft. One thing is - HVAC is usually considered as being a forced air system, yet with passive heating and cooling, air flow rates can exceed those of an active system. This is also in Wisconsin, where the summers are mild, and the winters can be brutal. We're situated for maintaining winter heat, with summer cooling as secondary.