One of the most important decisions in the air conditioner purchasing process is choosing the right size. Choosing either an under-sized or an over-sized air conditioner is problematic. An air conditioner that is too small is going to have serious problems cooling the space to the extent needed. In contrast, an air conditioner that is too big can cool the space but is also going to end up failing to remove the air’s moisture content. As a result, the air in the room being cooled is going end up feeling cold and damp rather than cool and refreshing.

Choosing the right size air conditioner is a simple process. You need nothing more than measuring tape, a calculator to run some basic calculations, plus pen and paper to record the results.

### How to Calculate Volume

First, you need to be able to calculate the volume of the space. Most spaces are going to be rectangular prisms, meaning that calculating their volumes is as simple as multiplying the length of the space by its width and then its height. For example, if you measure a room to find that its length is 12 feet long, its width is 8 feet long, and its height is 10 feet tall, then its height can be calculated to equal 960 square feet. In contrast, a space is the shape of a triangular prism uses the same formula except that the product is divided by two. Bear in mind that the height of a triangular prism is the tallest point of the space. More complicated shapes can require more complicated formulas. However, it is important to remember that shapes can often be broken up into pieces and that the pieces can be calculated individually.

### How to Calculate BTU

Once you have calculated the volume of the space that is going to be cooled, you can then calculate the BTU per hour needed to cool that space. BTU stands for British thermal unit. It is defined as being the amount of energy needed to heat one pound of water by one degree as measured in Fahrenheit. However, this is irrelevant.

For the most part, estimates can be used to figure out the BTU needed. For example, a space measuring 100 to 150 square feet needs 5,000 BTU per hour, a space measuring 100 to 250 square feet needs 6,000 BTU per hour, and so on. As a rough guideline, the BTU per hour needed for spaces measuring more than 350 square feet can be estimated as their volume multiplied by 25. You should use a search engine to find one of the numerous BTU calculators that are available if you are interested in getting more precise answers. Bear in mind that there are also some changes based on the space’s lighting and use. For example, a shaded space can be cooled using 10% less in BTU per hour while a space that experiences large amounts of sunlight must be cooled using 10% extra BTUs per hour. Similarly, a kitchen needs about 4,000 extra BTU per hour to be kept cool.

### Purchasing the Right Size Air Conditioner For a Home

Calculating the BTU per hour for a home rather than a space is simple. All that needs to be done is calculating the sum of the volume of the individual rooms in the home. The rest can be calculated using the same process.