# Size a Mini-Split System Air Conditioner and Calculate the Room Size for an Air Conditioner

Split-system air-conditioning units are deemed split because the fan and condenser are outside the building, and the evaporative coil and other components reside inside the building. This is typical of a window unit. Smaller units, or mini-systems, usually sit outside small dwellings, such as condos or work sheds, and they typically cool a 300- to 800-square-foot area.

**How to Size a Mini-Split System Air Conditioner**

You can size a small system by calculating the square footage of the rooms connected to the system and converting the calculation to tons. Measure each room individually for length and width. Multiply the length times the width to determine the square footage of the room.

Do not include areas closed off from the air-conditioning system, such as closets. Convert the square footage to British thermal units. Most bedrooms run 100 to 150 square feet, and that converts to 5,000 BTUs.

A 150- to 250-square foot room converts to 6,000 BTUs. Rooms running 250 to 350 square feet need 7,000 BTUs. Add 4,000 BTUs to kitchens and 1,000 BTUs to bathrooms because those rooms need additional cooling power.

Add each rooms total BTUs together to calculate the total number of BTUs needed for the whole area. Convert the total BTUs to tons, which is the measurement for all residential and commercial AC units regardless of size. One ton = 12,000 BTU per hour.

So, 18,000 BTUs equals 1. 5 tons, 24,000 BTUs equals 2 tons, 30,000 BTUs is 2. 5 tons, 36,000 BTUs converts to 3 tons, 42,000 BTUs is 3.

5 tons, 48,000 BTUs calls for a 4-ton unit, and 60,000 BTUs equals 5 tons. The ton size is the size of the air-conditioner unit needed to cool the area. .

**How to Calculate the Room Size for an Air Conditioner**

An air conditioner that is too small will not be able to cool the air sufficiently. It will have a tendency to be overworked, creating undue wear on the unit. Measure the space you will be cooling with a tape measure.

Find the length and width of the space. Multiply the length and width together for each room. Add each rooms total together to get the total area to be cooled by an air conditioner.

Do not forget to measure large bathrooms, entryways and hallways. These spaces will also need to be cooled. Divide the total area of the space that you are attempting to cool by 500 if it is residential and 400 if it is commercial.

The result is the number of tons you will need for your air conditioner. For example, if your residential space is 2,500 square feet, dividing 2,500 by 500 equals 5 tons needed.

The size and type of air conditioner needed depends on the size of space you are trying to cool. An air conditioner that is too large will cool the air too quickly and will not correctly handle the humidity level. An air conditioner that is too large also will have a tendency to turn on and off more often than really need, creating undo wear on the unit.

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