Buying Guide for a New Air Conditioner: Sizing

Buying Guide for a New Air Conditioner: SizingAir conditioner sizing: get it right before you buy or you may regret it for as long as you own the unit. “Sizing” in the HVAC sense doesn’t refer to physical dimensions. It means the capacity of the air conditioner; i.e., the amount of cooling it can produce expressed as BTUs of heat energy extracted from the air per hour.

The Capacity For Cool

Every air conditioner comes with a size rating. For example, a standard residential central A/C for a 2,000 square foot home in our climate zone might be sized at 3 “tons” of cooling capacity. Each ton of capacity = 12,000 BTUs per hour, so that unit is rated to extract 36,000 BTUs of heat from the house every hour.

Sizing Up Your House

But how much heat actually needs to be removed to keep your specific home comfortably cool? Square footage is only a very rough guideline that should never be the only factor. Every house is different. Variables include:

  • Basic floor plan
  • Daily sun exposure
  • Type of insulation
  • Number of occupants
  • Air-tightness of the structure
  • Number of windows

All the above comprise a comprehensive figure known as the home’s “cooling load.” Expressed in BTUs per hour, the cooling load represents the exact amount of air conditioner capacity required to keep the house comfortable on a typical hot summer day.

Why Load Matters

Cooling load is determined by a formal load calculation conducted by a qualified HVAC professional utilizing industry-standard load software. A precise load calculation gives the HVAC contractor the data needed for accurate air conditioner sizing— matching an A/C with the appropriate cooling capacity to meet the unique cooling requirements of your home. Rough guesstimates or rule-of-thumb averages aren’t good enough. Installing an over-sized or under-sized air conditioner means sub-standard cooling performance, higher monthly operating costs, poor air quality and greater wear and tear on system components. These negatives will persist until the unit is replaced.

For more about the importance of proper air conditioner sizing, contact Paitson Bros., your local source for trusted HVAC advice since 1922.

Our goal is to help educate our customers in Terre Haute, Indiana about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Guide or call us at 812-645-6859.

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