Calculate tonnage of heating and cooling equipment needed based on square footage of homes, such as 1 ton for every 1,000 square feet. Find the overall tonnage by factoring several criteria such as number of windows, people in the house, thermal properties of appliances and overall heat gain of the dwelling.
- Use a rule of thumb
Know the general rule of thumb for newer homes in the United States, which is 1 ton of equipment for every 1,000 square feet of living space. Realize that energy-efficient homes may only need 1 ton for every 2,000 square feet.
- Take into account different variables
Calculate variables that add heat to a home. A human body averages 230 BTUs per hour. The total amount of appliances account for 1,600 BTUs in an hour, and lighting adds another 1,600 BTUH. Houses with more efficient appliances, fewer windows and better lighting do not have as much inside heat. Denote that heating and cooling zones mean different needs based on local climates. Square footage needs for HVAC equipment differs from warmer climates to cooler climates in the United States.
- Find tools to help
Get assistance from computer programs that help by automating the process. Find programs that follow the "Manual J" method adopted by the Air Conditioning Contractors of America. When calculations are done correctly, the computer program determines a smaller air conditioner is needed than what is normally calculated using a rule of thumb.