How to Calculate AC Tonnage

Air conditioning sizes are measured in tonnage.

The term tonnage can be traced back to the beginnings of refrigeration when ice was the only available means of cooling. It takes 1 ton of ice to absorb 288,000 Btu, British thermal units, of heat in a 24-hour period, or 12,000 Btuh, Btu per hour. Thanks to modern equipment, you can cool your home without the ice; however, you still have to calculate the cooling load in Btuh for your structure and then convert the figure to tonnage.

Things You'll Need

• Manual J load calculation form
• Calculator

Instructions

1. Calculate the total cooling load in Btuh for your structure using a load calculating program or a form "J-1---Load Calculation for Residential Air Conditioning." The "J-1" form, by Air Conditioning Contractors of America, is the industry standard. Most software programs use the same calculations.

2. Divide the total Btuh cooling load by 12,000. A ton of cooling is equal to 12,000 Btuh.

3. Round your number up to a standard tonnage. Standard tonnage for residential equipment is 1.5, 2, 2.5, 3, 3.5, 4 and 5.

Tips & Warnings

• Both the manual containing the "J-1" form, "Load Calculation for Residential Summer and Winter Air Conditioning," and load calculation software can be purchased from most contractor bookstores.

References

• "Load Calculation for Commercial Summer and Winter Air Conditioning"; ACCA; 1988
• "Audels Refrigeration and Air Conditioning Guide"; Edwin P. Anderson; 1944

Resources

• Air Conditioning Contractors of America: ACCA Home Page