Residential Plumbing & HVAC Experts

Why Load Calculations Matter Before Any HVAC Purchases Occur

The initial cost of an HVAC purchase and installation, such as an A/C or heat pump upgrade, depends largely on the size, quality and features installed, and choosing the correct system size depends on bottom-line load calculations with no fudging the figures. On the flip side of the coin for actual long-term costs and reasonably fast return on investment, the home’s cooling/heating load, A/C- or heat pump-system capacity and good ductwork configuration all must be sound in design, since they all depend on one another.

Load calculations matter

Manual J is the HVAC industry standard for load calculations. Manual J was developed by the Air Conditioning Contractors of America, and is endorsed by local, state and federal agencies and the American National Standards Institute (ANSI). Factors that go into Manual J calculations include:

  • Calculating the square footage, window size and number, floor plan, ceiling height, ductwork design, building materials and much more of your home
  • Local climate including relative humidity, average temperatures and solar gain
  • Using sophisticated equipment to measure air leaks and insulation efficiency
  • Considering occupants in regard to number, age, energy habits and schedule
  • Taking into account the heat generated from appliances and lighting

System capacity

The size, or capacity, of your new A/C or heat pump is determined, using Manual S, based on the cooling/heating load (Manual J) the equipment needs to satisfy. Sizing is also affected by integrated systems and A/C or heat pump features including the following:

  • Zoning system
  • Whole-house humidifier
  • Variable-speed air handler
  • Two-stage compressor
  • Smart thermostats

Ductwork design

The design of the ductwork is considered as a component of load calculations because ducts play a large role in energy efficiency. There is a vast difference in cooling and heating bills and home comfort between a poorly designed duct system, and a proper duct system that utilizes the following criteria:

  • Duct branches use conditioned spaces
  • Duct branches are short and straight, utilizing inner walls for outlets and grilles
  • Return grilles are installed near supply outlets for balanced air flow
  • Duct joints are impermeably sealed with screws, mastic sealant and metal tape

For more information about load calculations and HVAC system purchase and installation, please contact us at Sherlock Heating and Air Conditioning. We serve homeowners in the greater San Diego area and southern Riverside County.