How to Determine the Size of Your A/C

One of the most important things in any home during the summer months is having a properly sized air conditioning (A/C) system. When installing an A/C system, it is critical that it's large enough to properly cool your home and protect the equipment from wearing out. However, a unit that is too large will not be energy efficient and may be louder than you desire. A/C units commonly are measured and sold by the ton. A few simple calculations will help you determine the size of your A/C system.

Measuring tape
Calculator

Instructions

- 1
  Determine the square footage of your home. Start in the main living quarters. Measure the length and width, and multiply them together to determine the square footage of the room. If the room is not square, divide it into multiple smaller rectangles and find the area of each.
- 2
  Calculate the BTUs needed to cool the room. Start with 5,000 BTUs for rooms that are 150 square feet and under. If the room is larger that 150 square feet, add 1,000 BTUs for each additional 100 square feet.
- 3
  Determine how many people normally will occupy the room. If more than two people, add 600 BTUs for each additional person.
- 4
  Decide how much sun the room gets throughout the normal course of a day. For rooms with much sun exposure, multiply the total BTUs by 1.1. For rooms that get less sun, multiply the BTUs by 0.9. This will be the total BTUs needed for the room.
- 5
  Repeat the process for each room in your home. Add an additional 4,000 BTUs to the final kitchen calculation, due to the heat that comes from cooking.
- 6
  Add together the BTUs for each room to determine the total needed for your home. Divide this number by 12,000. This will determine the A/C size you need in tons.

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