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How to Size an Air Conditioner

A new air conditioner for your home holds the promise of greater comfort all summer. Air conditioner manufacturers have also made great strides in efficiency. As a result, you can expect your new air conditioner to outperform your old system. To enjoy the best results, you must know how to size an air conditioner. They come in different sizes for a reason. A mismatch between equipment and building size produces poor temperature control and high electric bills.

Tools NeededHow to Size an Air Conditioner

  • Measuring tape
  • Paper and pencil
  • Calculator

Btu and SEER Ratings

On the most basic level, how to size an air conditioner comes down to figuring out the correct Btu number. Btu, short for British thermal unit, describes the amount of energy used to change the temperature of a ton of air. In general, an air conditioner must use 12,000 Btu of energy to pull heat out of one ton of air. The size of your home determines how many tons of air occupies the space inside. Different sizes of air conditioners have different Btu ratings to describe how much air a machine can condition.

Seasonal Energy Efficiency Ratio (SEER), on the other hand, describes the overall energy efficiency of the machine. SEER varies with the region because some climates place lower demands on an air conditioner than extremely hot locations. SEER explains the relationship between cooling output and energy consumption. A higher SEER number means better energy efficiency.

How to Size an Air Conditioner Step by Step

  1. Find out the square footage of your home.
  2. Draw a basic diagram of your house’s perimeter.
  3. Separate different sections or wings into rectangles that you can measure.
  4. Measure the length and width of each section of your home.
  5. Write down the dimensions on your sketch.
  6. Multiple the length and width of each section to obtain the square footage.
  7. Add up the square footage of each section to find the total square footage of your home.
  8. Find the estimated air tonnage for your total square footage.
  • Up to 1,000 square feet equals 1.5 tons
  • 1,000 to 1,500 square feet equals 2 tons
  • 1,500 to 2,000 square feet equals 3 tons
  • 2,000 to 2,500 square feet equals 4 tons
  • 2,500 to 3,300 square feet equals 5 tons
  1. Once you know the air tonnage for your home, narrow your focus on air conditioner models with the appropriate Btu capacity.
  2. The next part of how to size an air conditioner looks at other factors.
  3. Consider how well your home is insulated. Poor insulation means you should select an air conditioner with more Btu.
  4. If your home has high sun exposure with little to no shade, you may need to increase your Btu.
  5. The existing ductwork in your home can impact performance as well. If the duct design has insufficient air returns, you would want to consult an air conditioner technician. A professional from Oliver can recommend how to improve the system or suggest an AC model that is a good fit.
  6. Compare the SEER ratings on the air conditioner models in your size range.
  7. Make a decision about the efficiency you desire. Greater efficiency costs more upfront for the equipment. A lower SEER rating, however, means you can expect higher operating costs.

Optimize Your New Air Conditioner with Oliver

The air conditioning specialists at Oliver take into account factors beyond the basics of square footage. We’ll help you evaluate all your home’s characteristics. Building materials and the condition of doors and windows also affect cooling performance. Contact us today for a new air conditioner quote.

Need help with this project?

If you do not have the time, tools, or experience necessary to complete the project, please contact the professionals at Oliver for help.

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