How to Calculate the Size of an AC Unit for a House
A correctly sized air conditioning unit is needed to keep your home cool and minimize your utility bills. If your AC unit is too small, it will fail to adequately cool your home and will break down rapidly because of over-stressing it. If it is too large, it will cool quickly but waste energy turning itself on and off often. The size of your AC unit for your home, also known as a central AC unit, is determined by the square footage of your home, how your rooms are used and how your home is built. Does this Spark an idea?
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Instructions
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1
Determine the square footage of your home. You can either check your blueprints or measure the square footage of each room. To calculate the square footage of a room, multiply the length times the width.
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2
Determine the base BTU by using a room sizing chart that can be found online (see Resources section). BTU stands for British thermal units and is a common energy measurement associated with the size of air conditioning units. For example, a 900 square foot home would need about 18,000 BTU.
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3
Amend your estimation in Step 2 if any of the rooms in your home is subjected to significant sunlight or is well shaded. For these rooms, calculate the square footage and then use the room sizing chart (see Resources section) to figure the BTU that the room would normally require. If the room is sunny, add 10 percent of that value. If it is shady, subtract 10 percent of that value.
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4
Add 4,000 BTU for each room that is not insulated.
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5
Add the values from Steps 2 through 5 to find the total BTU capacity needed for your AC unit. Because some AC units list their size in tons rather than BTU, you may need to convert your units. You can convert from BTU to tons by dividing by 12,000. For example, 24,000 BTU would be equivalent to 2 tons.
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