How to Determine Size of AC Unit in a House
Sizing your home for an AC unit is a relatively easy task. You can do some math in your head to arrive at the proper tonnage and British thermal unit (BTU) capacity for your new air-conditioning unit. However, measuring the size of your home is not sufficient to determine the size of the AC unit. There are other considerations, but they are simple if you pay attention to how the sun heats your home. You can have your calculations done in 5 or 10 minutes and then be off looking at new AC units for your home. Does this Spark an idea?
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Instructions
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Obtain the total square footage of the home. Include any area that has an air duct in it. You can do this by going to your county appraiser's website, through blueprints of your home or by measuring each room's length and width and multiplying those numbers for area, then adding up the area of the rooms.
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Use the chart from Energy Star to determine the base BTUs your air conditioner needs to be. For example, if your measurements come to between 700 and 1,000 square feet, you will need a central air conditioner capable of handling 18,000 BTUs per hour.
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Make the necessary adjustments for insulation, kitchens, shade and sunny sides of the home. Add 4,000 BTUs for each room that does not have an insulated ceiling. Add 4,000 BTUs for each kitchen in the home. Account for a shady room by subtracting 10 percent from the BTUs necessary for that room (refer to the Energy Star chart for BTUs for individual room sizes); account for a sunny room by adding 10 percent to that room's BTU capacity. If a room will normally be occupied by more than two people, say your living room, increase capacity by 600 BTUs for each additional person.
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Total the BTUs you have calculated for your home. You can buy your new air conditioner according to the BTUs, or you can convert that number into how many tons the new AC can handle. One ton is equal to 12,000 BTUs, so if you arrive at 18,000 BTUs for your home, you will need to buy a 1.5 ton AC unit.
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Tips & Warnings
Do not oversize your unit. This does not make the AC run more efficiently or make the home cooler. It only increases your electric bill.
