When it comes to selecting your window air conditioner, choosing the right size is the most important decision you will make. Selecting a unit too small will be too underpowered to cool your room, and you will never reach the cool temperatures you are looking for.
On the other hand, picking an oversized unit will cool the room quickly, but will inefficiently cycle on and off costing you extra money. Window air conditioners also dehumidify the air on top of cooling it. An overpowered unit will run less often leaving more humidity in the air and your room feeling muggy.
Room air conditioners receive a BTU rating, starting from around 5,000 BTUs all the way up to the most powerful around 36,000 BTUs. Once we calculate the square footage of the space we want to cool, we can decide on how powerful of a unit we need to go after. In this article, we will look at measuring and calculating our space below and then compare our calculation to the BTU conversion chart (Shown Below) to determine our BTU rating.
The first step in choosing a room air conditioner is measuring your space to calculate square feet. To get the right number you will need to do some measuring and a little geometry. So, let us cover a couple simple geometric formulas to get us started.
The formula used to calculate the square footage of a typical square or rectangular is going to be the formula used for most rooms. This formula is simple:
L x B = Square Footage
Selecting the BTU Rating of Our Room Air Conditioner
Comparing our calculation to the chart below, we see that 290 sq ft comes in at the high end of a 7,000 BTU unit. You will not find a great selection of window air conditioners at the 7,000 BTU Range, but we are very close to the 8,000 BTU range as well, and moving to that BTU range is justifiable in this case.
BTU Chart Based on Room Size
|Room Size||BTU’s Needed||Room Size||BTU’s Needed|
|150 sq. ft.||5,000 BTU’s||700 sq. ft.||14,000 BTU’s|
|250 sq. ft.||6,000 BTU’s||1,000 sq. ft.||18,000 BTU’s|
|300 sq. ft.||7,000 BTU’s||1,200 sq. ft.||21,000 BTU’s|
|350 sq. ft.||8,000 BTU’s||1,400 sq. ft.||23,000 BTU’s|
|400 sq. ft.||9,000 BTU’s||1,600 sq. ft.||25,000 BTU’s|
|450 sq. ft.||10,000 BTU’s||1,900 sq. ft.||28,000 BTU’s|
|550 sq. ft.||12,000 BTU’s||2,700 sq. ft.||36,000 BTU’s|
To determine the most accurate BTU estimate, you should also consider these factors:
- Ceiling Height
The above estimates assume you have traditional 8-foot ceilings. If your ceilings measure higher than 8 feet, you’ll want to increase your BTU level.
If your room or space is sunny during the day, increase your BTUs by 10 percent.
If your room is shaded for most of the day, decrease your BTUs by 10 percent.
- Number of Occupants
If more than 2 people will occupy your room or space regularly, you should add an additional 600 BTUs of cooling power for each person.
If you are installing your window AC in a kitchen, increase the BTU level by 4,000.
One of the most common mistakes in selecting a room air conditioning unit is the purchase of an underpowered unit that will not properly cool the room. With the proper measurements and calculations, you will be able to determine the square footage of your room and make the wise choice for your next room AC.