A/C Sizing: A Quick Primer On Manual J

No amount of equipment efficiency or ductwork design can compensate for a system that’s under- or over-sized for your needs. That’s why the first crucial step to installing heating and cooling into a new home, or upgrading an existing system, is to have the required heating and cooling load for your residence calculated to properly size the optimum system.

This calculation utilizes load formulas incorporated in Manual J, the Air Conditioning Contractors of America’s industry standard for sizing HVAC systems. It’s a complex job for HVAC professionals, not something you want to work out with pencil and paper. Manual J calculations are based on three parameters:

  • Sensible cooling load
  • Heating load
  • Latent cooling load
  • The first two describe, respectively, the amount of cooling or heating required to maintain an expected level of comfort during maximum demand conditions. Latent cooling load is the amount of humidity that must be removed to preserve comfort standards in a peak load scenario—like a hot, humid south central Texas summer day.

    The Manual J calculation is customized to your residence by a number of factors:

    • Square footage and shape of the home
    • Amount and R-rating of installed insulation
    • Overall air-tightness of the structure
    • Number and size of windows and their orientation to the sun
    • Wattage of lights and the category of bulbs
    • Large appliances in use
    • Number of occupants and their ages
    • Local climate

    The final Manual J calculation provides your HVAC contractor with the data he needs to select the equipment with the capacity to meet your needs.

    Beyer Boys is San Antonio’s local source for experienced sales and service backed by accurate facts and figures. Give us a call for all your interior comfort needs. We’ve been serving area residents since 1990.

    Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).

    Beyer Boys services San Antonio, TX. Visit our website to see our special offers and get started today!

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