Unlike a central AC unit, which cools your entire home, an AC window unit is used to cool a specific room. If you only want to cool certain rooms, using an AC window unit is more energy efficient than a central AC unit.

To maximize your energy efficiency, it’s important to choose the right-sized unit. When it comes to choosing an energy efficient AC window unit, **bigger is not always better**. Choosing the wrong size could decrease the AC unit’s effectiveness and waste a significant amount of energy. Here’s how to determine which size is right for your room:

## Calculate the Room’s Square Footage

You will need a unit that is large enough to cool the entire room, but not so big that it wastes energy. The first step in figuring out which size is right for you is measuring the square footage of the room.

The formula to calculate the square footage will depend on the shape of the room. Use these formulas:

**Square or rectangular rooms:**Multiple the length of the room by the width of the room.**Triangular rooms:**Multiple the length of the room by the width of the room. Then, divide this number by two.**Oddly shaped rooms:**It’s a bit more difficult to calculate the square footage if your room is not square, rectangular, or triangular. Divide the space into small triangles, rectangles, and squares. Use the formulas for square, rectangular, and triangular shaped rooms to calculate the square footage of each section. Then, add all of these measurements together to get the total square footage of the entire room.

It’s important to note that **all measurements should be in feet, not inches**. For example, if your room is 15 feet and 9 inches wide, the correct measurement would be 15.75 feet.

## Determine the Correct Cooling Capacity

The next step is determining the appropriate cooling capacity for your energy efficient window air conditioner unit. Every air conditioner comes with a British Thermal Unit, or BTU rating, which indicates the unit’s cooling power. The BTU rating is a measure of the amount of heat that an air conditioner unit is capable of removing from the room per hour. The higher the BTU rating, the more powerful the unit.

However, this does not mean you should simply choose the unit with the highest BTU rating. Instead, it’s important to **choose a unit with a BTU rating that is appropriate for the size of your room**. Here’s what BTU rating, or cooling capacity, the Department of Energy recommends for rooms of various sizes:

- Between 100 to 150 square feet: 5,000 BTUs
- Between 150 to 250 square feet: 6,000 BTUs
- Between 250 to 300 square feet: 7,000 BTUs
- Between 300 to 350 square feet: 8,000 BTUs
- Between 350 to 400 square feet: 9,000 BTUs
- Between 400 to 450 square feet: 10,000 BTUs
- Between 450 to 550 square feet: 12,000 BTUs
- Between 550 to 700 square feet: 14,000 BTUs
- Between 700 to 1,000 square feet: 18,000 BTUs

For example, if your room is 500 square feet, the Department of Energy recommends finding an energy efficient AC window unit with a cooling capacity of 12,000 BTUs per hour.

Following these recommendations will ensure you pick a unit that is **capable of keeping your room cool ****without wasting energy**.

## Make Necessary Adjustments

The Department of Energy’s cooling capacity recommendations can be used in the vast majority of cases. But under certain circumstances, you may need a larger or smaller cooling capacity than what the Department of Energy recommends. Make the necessary adjustments to your cooling capacity for these circumstances:

- If the room does not get a lot of natural light, you can
**reduce your recommended cooling capacity by 10%**. - If the room gets a significant amount of natural light, you should
**increase your recommended cooling capacity by 10%**. - If you intend on using the unit in your kitchen,
**add 4,000 BTUs to your recommended cooling capacity.** - If the room is typically occupied by more than two people, you may need an energy efficient window air conditioner with a larger cooling capacity. You should
**increase your recommended cooling capacity by 600 BTUs for every additional person**who occupies the room. For example, if three people usually occupy the room, you would need an additional 600 BTUs, but if four people usually occupy the room, you would need an additional 1200 BTUs.

Follow these tips to ensure you can find the most energy efficient window air conditioner for your home. Installing your new unit will help you **save energy, ****lower your monthly utility bills****, and ****reduce your carbon footprint****!**