The Size of a Ductless Air Conditioner for a Thousand Square Foot Apartment

Base BTU Capacity

• To select the right size of ductless air conditioner, you need to calculate the British Thermal Unit (BTU) capacity. The BTU determines how much heat the air conditioner can move and cool in one hour. Energy Star.gov recommends a base BTU capacity of 21,000 for a space that measures from 1,000 to 1,200 square feet.

Windows

• Once you know the base BTU number, you need to factor in the amount of windows in your apartment for the size of ductless air conditioner you will need. Energy Star recommends that you add 1,000 BTU for every window in each room of your home. Let's assume that your 1,000 square foot apartment has one bedroom with two windows, two windows in the living room, two windows in the kitchen and one window in the bathroom for a total of seven windows. Add 7,000 to the base BTU capacity of 21,000 to get a new BTU subtotal of 28,000.

Occupants

• Making sure that everyone is comfortable means accounting for the total number of occupants in the apartment when you calculate the size of your air conditioner. Energy Star recommends that you add 400 BTU for every person who lives in your home. In our 1,000 square foot home apartment, we'll assume there are two occupants and add 800 to get a new BTU subtotal of 28,800.

Kitchen

• You also have to factor in the extra heat that your kitchen generates (even if you don't cook frequently), by adding 4,000 BTU to the subtotal. This gives the 1,000 square foot apartment a new subtotal of 32,800.

Sunshine and Shade

• If your home is in an area with heavy shade, decrease the subtotal by 10 percent. On the other hand, if your home gets lots of sunshine, increase the subtotal by 10 percent. We'll assume that the apartment in our example gets lots of sunshine and add 3,280 (10 percent of 32,800) to get a new total of 36,080 BTU.

Estimated BTUs Per Hour and Cautions

• The 36,080 BTU total tells us that the air conditioner should be capable of generating 38,080 BTUs per hour (BTUh). Even though a ductless unit is less complicated than central air conditioning but more complicated than installing a window or room air conditioner, you still need to get an on-site estimate and have the air conditioner professionally installed. When you review the final estimate, avoid the common mistake of purchasing a unit that is larger than necessary. Bigger is not better when it comes to air conditioners. A unit that has more BTUh than you need will be more costly to operate as well as more expensive in terms of initial cost.