An HVAC system with components that are incorrectly installed or installed in ways that are disadvantageous is one that is poorly designed. Maximizing airflow across the heat exchanger unit ensures maximum heat transfer and maximum system efficiency. A heating, ventilation, and air conditioning system that is improperly installed will also detract from system efficiency. Placing the thermostat too near an air outlet or return, for example, will also cause efficiency to suffer. How installation affects HVAC system design will be discussed below in some detail. Safety and longevity concerns are also briefly discussed.
HVAC system components are generally divided between indoor and outdoor appliances, with the heat-producing, heaviest components such as the compressor and condenser coil located outside the home and the evaporator being installed in the plenum of the furnace, typically in the attic space, garage or other service location indoors. These indoor and outdoor segments are connected a low-voltage relay cable and refrigeration lines.