An oversized heating, ventilation and air conditioning, or HVAC, system which creates more coolness or heat in the event you need may sound like a benefit. However, the true result is a common complaint from the HVAC industry known as “short cycling.” Air conditioners and furnaces that brief cycle flip on and off quite rapidly. The results include noticeably diminished energy efficiency and increased component wear and tear. Short cycling happens when an HVAC system is too big for the home.
“Sizing” HVAC equipment describes matching the British thermal unit, or BTU, ability of the air conditioner and furnace into the home’s square footage and special thermal characteristics. Previously, when energy prices were less of an issue, it was common for contractors installing HVAC equipment to cut corners and just imagine the proper capacity instead of conducting a proper sizing procedure.
Not too Big, Not too Small
To accurately size an HVAC program today, a contractor uses Manual J, the industry standard sizing software. The program accepts thermal data, such as solar exposure, amount of insulation, number of windows and overall air-tightness of the structure, and creates a figure referred to as a load calculation that expresses the home’s heat loss and gain. Having an accurate load calculation, the contractor can match the requirements of the house to an HVAC system with the proper capacity and avoid oversizing and resultant short cycling.