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Sizing Considerations When Buying a New Air Conditioner

A row of little houses that range in sizes

When youandrsquo;re purchasing a new cooling system, youandrsquo;ll have to make a series of choices, the first, and most important, of which should be its size. Skipping the air conditioner sizing process could result in a system thatandrsquo;s too large or too small, both of which affect your homeandrsquo;s comfort in the summer and its cooling bills.


The HVAC industry has developed software called Manual J to accurately size HVAC systems for homes based on many factors that include:

  • Its cubic footage.
  • Levels of insulation in the attic and walls.
  • Number of windows, their placement, size and energy efficiency.
  • Orientation to the sun.
  • Floor plan design.
  • Air leakage rate.
  • Number of heat-producing appliances indoors.
  • Age and size of family.
  • Landscaping factors.

Each of these impacts the energy efficiency of your home. Once all the data are entered, the software returns a value for the recommended air conditioner sizing. The process does take time and it involves a thorough examination and analysis of your home.

WHATandrsquo;S AT RISK

When you install an air conditioner thatandrsquo;s the wrong size, you risk higher energy bills, less comfort and a shorter system lifetime. A system thatandrsquo;s too big will run in short cycles, which means that it doesnandrsquo;t run long enough in each cycle to reach its optimal running speed. Energy use will be higher because AC systems use the most power at startup. Humidity levels will remain high because the system wonandrsquo;t have enough time to condense the water vapor in the air.

Equipment thatandrsquo;s too small will struggle to cool your home during extremely hot weather. Even though itandrsquo;s not good, itandrsquo;s better to have a system thatandrsquo;s too small than too large. Humidity wonandrsquo;t be an issue and the system will reach optimal running speeds most of the time.

Most of the time, air conditioner sizing isnandrsquo;t a do-it-yourself project. If youandrsquo;d like to learn more, contact Valley Heating, Cooling, Electrical and Solar providing HVAC services for Santa Cruz and South Bay Peninsula homeowners. Visit our website or give us at call at (408) 868-5500.

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