Whether you are upgrading your existing HVAC system for energy efficiency or you are building a new home, understanding load calculation for your system is crucial. Load calculation is the process of evaluating the heating and cooling demand of your home to determine the size of HVAC equipment. HVAC equipment needs to be just the right size for the space and demand. A unit that is too small will never quite attain a comfortable temperature level, and a unit that is too big will consume more energy than necessary to heat and cool the home. If a unit is not sized appropriately for the space, the home may develop moisture problems, as well. An experienced professional HVAC service technician utilizes specific methodologies for load calculation based on external and indoor solutions.

Short Cycling

An HVAC system that is too big for the living space will tend to short cycle. Because the large system can quickly condition the air, the unit does not completely cycle. Short cycling can cause problems for the home and the equipment. The life of the HVAC equipment is shortened because the unit frequently turns on and off. During short cycling, the AC system does not run long enough to dehumidify the home. Therefore, the home may seem moist and clammy. Too much moisture in the air can cause structure rot, mold and other problems. Additionally, the extra tonnage costs additional money to install. Save money, preserve your HVAC equipment and ensure that your home is safe with a heating and air conditioning system sized just right for your home.

Manual J Calculations

HVAC load is calculated based on the protocol provided in Air Conditioning Contractors of America’s Manual J. Factors that are considered in the calculation of load in the Manual J protocol include:

  • Climate zone
  • Size of home
  • Directional orientation
  • Envelope of the house
  • U-Value of windows
  • Window size
  • Window overhang
  • Wall structure
  • Ceiling type
  • Number, condition of glass doors
  • Floor type
  • Number, type of doors
  • Ductwork conditions
  • Insulation

Additional factors include:

  • Number of people living in the home
  • Desired indoor temperature
  • Desired indoor humidity

Precise Calculations for Best Results

In years past, sizing HVAC equipment was performed by using “rule of thumb” estimates, such as X number of square feet of living space per ton of equipment. However, these rule of thumb estimates do not take into account factors such as how well the home is insulated and sealed or the number of people living in the home. Many Pine Mountain GA homes have HVAC equipment that is too big or too small for the environment.

Manual J calculations have increased in use in the past 10 or 15 years. Manual J calculations are generally performed with software applications. Software, such as Wrightsoft’s Right Suite Universal provide the HVAC installation specialist with a tool to calculate load. Web-based applications are also available. The technician enters the home’s data, and the program provides the optimal equipment size as the output. When you consider installing new HVAC equipment, be sure that your HVAC installation specialist uses Manual J calculations to properly estimate the size of equipment for your application.

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