Then, in the table included below,. To calculate the size of air conditioning you need, calculate the square footage of your home and multiply it by 20 to get the necessary BTUs. Every 12,000 BTU equals one ton. A good rule to follow is that if your house is well insulated and has new-style windows, you can (in most cases) safely choose the smallest size system that meets the necessary specifications for the total square footage.
If your home isn't well insulated or if you have old-style windows and an obscenely high number of windows, you'll want to select a larger system that falls within the specified square footage range. The first step is to calculate the square meters of your building or the rooms you want to cool. You'll need to calculate the square footage of the room where the air-conditioned window will be to determine what size you need. In most cases, you can use the following conversion information to help you determine the size of your current air conditioning system (use the system's model number, NOT the serial number).