Most homeowners take their HVAC and air conditioning equipment for granted. Truth be told, modern, sophisticated heating pumps and A/C unit can robustly withstand a lot and keep their efficiency. But even the best machines out there will degrade. An average A/C unit, for instance, might lose five percent of its capacity annually. Thus, say you built your home with a 14 SEER unit A/C several years ago. Today, that unit might only function at 10 SEER capacity.