How to Tell What Size AC Unit You Need

Whether you are looking for an air conditioner (AC unit) that fits in the wall, a window or a portable unit, you need to take the correct measurements of the room or rooms that the unit will cool. Using a smaller British thermal unit (BTU) appliance for the cooling area will result in constant running of the air conditioner and probably will not cool the entire area correctly. If you choose an AC unit that has more BTUs than what you need, you will waste energy. Determine what size AC unit you need before you do any shopping.

Tell What Size AC Unit You Need
  1. Measure the room or rooms where you will use the AC unit. Measure the width and length of the room. If you are buying the unit for the entire home, you measure slightly differently. If measuring the entire house, measure from one end of the house to the other end for length and then measure one end to the other for width.

  2. Calculate your measurements into square footage. Multiply the length by the width to determine the square feet. For instance, a room that is 13 feet wide and 15 feet long will equal 195 square feet. If you have two floors to cool, repeat the process for the second floor.

  3. Look at the BTU chart to determine the size of the air conditioning unit you need. Keep in mind that if you need more than 32,000 BTUs, a central air system is a better choice. If you have a two-story home and are not choosing central air, you will need a unit on each floor. Cold air does not rise.

  4. Add 10 percent BTUs if the room you plan to cool is a sunny room, unless you can use shades and blinds to block out the sun. If the room will have more than two people occupying it, add 600 BTUs to your total. If you are using a portable unit in a kitchen, add 4,000 BTUs for the heat generated from appliances and cooking.

About the Author

Pamela Gardapee is a writer with more than seven years experience writing Web content. Being functional in finances, home projects and computers has allowed Gardapee to give her readers valuable information. She studied accounting, computers and writing before offering her tax, computer and writing services to others.