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Central Air Conditioning Unit Size (AC)

Determining the Right Central Air Conditioning Size (AC)

Air conditioner size is rated using the number of BTU's or British Thermal Units of heat that it can remove per hour. (1 BTU is the amount of energy to raise the temperature of one pound of water by one degree Fahrenheit.) You may also hear ac size referred to in "tons" which is the equivalent of 12,000 BTU's. (12,000 BTU's is the amount of energy required to melt 1 ton of ice in one day.) An average central air conditioner size would be between 3-6 ton or 36,000 - 72,000 BTU's/hr. Note: the size or capacity is not directly related to how efficient an air conditioner is.

In order to determine the correct size of central air conditioner for your home you must consider:

  • Local climate
  • Age and size of your home
  • How many windows and size of the windows in your home
  • Level of insulation your home has
  • Level of shade that falls on your house walls, windows and roof
  • Direction that your home faces

While the above may seem like overkill it really isn't, here's why. In order for your ac unit to work as efficiently as possible it must be carefully sized to your specific house and environment.

Installing an air conditioner that is too small will result in:

  • Increased energy bills since the unit must run additional hours trying to keep up with the heat of the house.
  • A home that is not comfortable since the unit is unable to cool quickly enough to "get on top" of the heat.

If you install a central air conditioner that is too large the unit will cycle (turn off and on) too often which will result in:

  • Less humidity being taken out of he air in the house. In a humid climate de-humidification is essential to the temperature feeling comfortable.
  • Less consistent temperature in the house.
  • More wear and tear on the ac compressor and other parts of the unit.

If you would like to get a rough idea of the size needed for a portable unit look at the chart on our portable air conditioning size page.

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