Summer is on the way, and that means that it's time to make sure your home has a reliable cooling system in place. If you are in the market for a window air conditioner, it is important to choose a unit that fits your space, and has a BTU number that suits your situation. Read on to learn all about how to size an air conditioner.

Summer is on the way, and that means that it's time to make sure your home has a reliable cooling system in place. If you are in the market for a window air conditioner, it is important to choose a unit that fits your space, and has a BTU number that suits your situation. Read on to learn all about how to size an air conditioner.

• Size is a very important consideration when purchasing a new air conditioner. Many people end up with a unit that is either too large or too small for their needs; both can be inefficient, and are liable to break down. Selecting the right size air conditioner will save you money on energy and repair bills, and will also help out the environment. Please note that this is a guide for measuring window AC's. If you are installing central air, there are numerous factors to consider, and the best thing to do is to contact a professional contractor.

• The first thing you will need to do is measure the dimensions of your room. Get a good tape measure and some writing materials, and measure to the nearest foot:

1. Room length
2. Room width
3. Height of the room (you may need a step ladder or chair to stand on)

• Multiply all of these numbers, and you will have the volume of the room. You can repeat this step in all rooms in your home, and then add them together to get the total volume of your house or apartment.

(Creative Commons photo by Inga Munsinger Cotton)

• The climate you live in will affect your sizing choice. The hotter your region, the more power you will need. The direction your room faces contributes to the overall climate of the space, as well. Rooms that are exposed mainly to the east or west will get hotter than northern or southern facing rooms, because they are exposed to direct sunlight in the morning or evening.

• How well insulated is the room? A well-insulated space will require a smaller air conditioning unit, and vice-versa. If you're not sure how good your insulation is, consider how well your home retains its temperature in severe weather. Do you ever feel a breeze when it is extremely windy? If so, your insulation is probably not great.

• Now that you have the basic information, you can figure out how many BTU's you need your air conditioner to have. You can use a chart such as this one to get a basic idea of how many BTU's are necessary. Make the number smaller or larger, depending on how you answered steps 2 and 3.

• Before you head out to buy your air conditioner, measure the dimensions of the window that you will be installing it into. Get the measurements of the height, width and depth of the space under the glass when the window is open.

• If you want some extra help, try an online sizing calculator. Here are a couple of resources:

1. Consumer Reports Worksheet
2. Good Housekeeping Calculator

• Selecting a correctly-sized air conditioning unit will save you money and produce less pollution than choosing one that is too large or too small. Just use the formula above to determine how many BTU's you will need, and then take the measurements of your window to figure out the physical dimensions to look for in your new AC unit. If you have special circumstances, or are unsure of your math skills, the best thing to do is to call a professional for help.

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• Introduction
• Step 1: Measure the Room
• Step 2: Think About Climate
• Step 3: Rate Insulation
• Step 4: Add it Up
• Step 4: Measure the Window