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NC State Extension

HVAC – Defined

Heating, Ventilation, and Air Conditioning – The mechanical systems that provide thermal comfort and air quality in an indoor space are often grouped together because they are generally interconnected. HVAC systems include central air conditioners, heat pumps, furnaces, boilers, rooftop units, chillers, and packaged systems. Right-size Heating and Cooling Equipment


Source:  Used with permission from Air Tech – HVAC Incorporated (

Bigger Is Not Better
The choice of a heating and cooling system that closely matches the homes load conditions is paramount to ensuring proper performance and comfort. A properly sized system should operate for longer periods as the outdoor temperature approaches the design temperature. At the design temperature, the system should run at or near 100% of the time while maintaining the designed indoor temperature. On rare occasions when outdoor design temperatures are exceeded, indoor design temperatures may not be maintained. This condition should only be temporary and does not warrant increased sizing because of the potential for short cycling, premature failure and higher than intended operating costs. Short cycling is the phenomenon of meeting the thermostats setting too quickly to properly filter, mix or dehumidify indoor air. The typical air conditioning system must run 8-10 minutes before the dehumidification process begins. When the system is oversized, the dehumidification process is almost eliminated until outdoor temperatures are high enough to create long run times. Premature equipment failure, increased repair costs and high operating costs can also be expected due to the increased stress and decreased efficiency of a starting and stopping motor, much like a car used for city driving versus highway driving.