Air Conditioning and Heating Sizing?

How many tons of air conditioning and heating do I need per square foot?

To accurately determine air conditioning and heating sizes you should perform a heat gain/loss calculation for the area you want to condition which will give you the required BTUs of air conditioning and heating needed. Many factors contribute to determine the size of air conditioning and heating BTU amount and include square feet of structure, type and size of windows/doors, insulation value, ceiling height, color of roof, number of occupants, ect. There are so many factors it can be confusing even for professionals. Professional HVAC estimators use software based on Manual "J" for residential and Manual "N" for commercial load calculations. After the sizing calculations are complete another Manual is used to properly size the duct work for the size of the equipment and application.

HVAC Sizing Rules of Thumb

It is not uncommon for HVAC estimators or HVAC contractors to use various rudimentary techniques which are generally referred to as rules of thumb. Some will say on the low end you need 1 ton of cooling for every 500 square feet. On the high end you will need 1 ton of cooling for every 700 square feet. These rules of thumb will also generally take into account a basic heat gain calculation for the kitchen and the number of people who will occupy the structure. At best these rules of thumb are educated guesses and may not give you an accurate calculation of what you really need. Unless the contractor used software based on the above mentioned manuals it would be to your advantage to actually do a proper load calculation for the structure based on Manual "J" or Manual "N" whichever is appropriate for your HVAC application.

Air Conditioner and Heating Ductwork Sizing

Manual "D" is used for sizing residential ductwork for the appropriate amount of airflow. For each ton of air conditioning you will need 400 cubic feet per minute (CFM) of airflow. It is imperative that this amount of airflow (400 CFM) be provided to the air conditioner evaporator coil of the air conditioning system. If the ductwork is too small it will restrict the amount of airflow crossing the air conditioner evaporator coil and this will likely cause big problems. If the ductwork is too big the system may have a problem generating enough static pressure to maintain designed airflow across the coil. The proper design and construction of the air conditioning and heating duct work is important for the proper functioning of the system. Using the proper techniques, software, and skilled personal will ensure that the HVAC job is accomplished correctly and will provide many years of reliable and efficient comfort to you.

Using good and time tested methods to size air conditioning and heating systems for your home or business is a smart thing to do. Using an HVAC estimator who is going to employ a rule of thumb for something that will be attached to your home and provide you with comfort for 15 to 20 years is not so smart. Use proper HVAC sizing methods and you will be better off and comfortable in the future.

Comments (0)

Name

Title

Comment

smaller | bigger

Subscribe via email (Registered users only)

I have read and agree to the Terms of Usage.

Write the displayed characters

Add Comment