Calculating Your Air Conditioner’s Size: Methods Your Technician Will Use

One of the most important things to do before you buy a new air conditioner for your San Antonio-area home is calculating your air conditioner’s size. An under- or oversized A/C system will cost you extra money and waste energy. It will also perform poorly—failing to keep your house consistently cool. It may even produce excessive noise. To determine the proper size for your new cooling system, your HVAC contractor must use an exacting, complex formula.

The formula, called a load calculation, is found in the Air Conditioning Contractors Association of America’s Manuals J and D. Be sure that your chosen home comfort contractor uses this methodology when he’s calculating your air conditioner’s size.

No guessing allowed

Using a rule of thumb or estimated load calculations is unacceptable. It doesn’t take your actual home’s specifics into account. Simply buying new cooling equipment in the same size as your old system won’t work either. Your home is likely better insulated now than in the past, with different cooling requirements. Only precise industry standards for calculating your air conditioner’s size ensure that you’ll get a properly sized air conditioner for your home and family needs.

Calculating your air conditioner’s size

Using Manual J’s methods, your HVAC contractor learns how much heat loss occurs in wintertime through the house’s exterior and the amount of heat gain in warmer months. If your home has an adequate duct system, whole-house or block load calculations are necessary, based on:

  • Local climate data.
  • Size, layout and position of the house on the lot.
  • Construction materials used.
  • Insulation R-values.
  • Window size, type and location.
  • Airtightness of the home/level of air infiltration.
  • Your family’s comfort preferences/usage patterns.

Manual D for duct design

When a new duct design is needed, your contractor should perform room-by-room calculations. This information guides the design of the new system, including individual duct sizing and layout.

When you need a new cooling system or repairs, contact Beyer Boys. Our experts have been providing complete HVAC services to the San Antonio community since 1990. Visit our website for valuable home-comfort advice and energy efficiency information, or just call us.

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).

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