Air Conditioner Sizing: The ABC’s Of Manual J

Air Conditioner Sizing: The ABC’s Of Manual J

Choosing a new air conditioner requires careful consideration of the size of your home and how much cooling it needs. The air conditioner must be properly sized—not too big and not too small—and must operate as efficiently and economically as possible. The unit must also be able to meet the “load” of your home, the actual amount of cooling that will be needed to keep your living spaces comfortable.

To determine your home’s cooling load, your HVAC contractor should conduct a load calculation using the industry-standard Manual J, “Residential Load Calculation.” This manual, published by the Air Conditioning Contractors of America (ACCA), sets forth all the standards, procedures and technical details of how to perform heating and cooling load calculations. It was developed by HVAC engineers and has been repeatedly validated through real-world applications.

A load calculation based on Manual J provides two pieces of information needed to correctly size your new or replacement air conditioner:

• Sensible cooling load: Sensible heat is the amount of heat that can be sensed, or detected with a thermometer. The sensible cooling load is the amount of this type of heat that your cooling system should be able to remove in the daytime during high-temperature days.
• Latent cooling load: Latent cooling load refers to the amount of moisture the cooling system should be able to remove during hot, wet, highly humid summer days. Latent cooling load determines the amount of energy needed to dehumidify your home’s indoor air during these extreme conditions.

Your HVAC contractor will base his equipment recommendations on the combination of sensible and latent cooling load data. Cooling equipment should be able to provide plenty of latent and sensible cooling, and it should be no more than 15 percent oversized based on these loads.

Contact Air-Tro today for more information on conducting heating and cooling load calculations for your home and why Manual J is the industry’s most trusted source for these calculations. We’ve been serving the greater Los Angeles area since 1969.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems).  For more information about air conditioners and other HVAC topics, visit our website.

Air-Tro Inc. services the greater Los Angeles area as well as the metro areas of Riverside and San Bernardino County.