Window AC Size Chart: What BTU Fits Your Room

The ENERGY STAR chart, read from the unit's side

ENERGY STAR says room air conditioner sizing is all about matching the room size to the air conditioner size. For a square or rectangular room, it says to multiply the full length by the width, measured in feet. For a room with a complex shape, it says to split the area into squares, rectangles and triangles and add the parts.

The chart pairs each band of floor area with a capacity. Read from the unit's side, it says which rooms each size covers, in square feet:

• 5,000 BTU per hour: 100 up to 150.
• 6,000 BTU per hour: 150 up to 250.
• 7,000 BTU per hour: 250 up to 300.
• 8,000 BTU per hour: 300 up to 350.
• 9,000 BTU per hour: 350 up to 400.
• 10,000 BTU per hour: 400 up to 450.
• 12,000 BTU per hour: 450 up to 550.
• 14,000 BTU per hour: 550 up to 700.
• 18,000 BTU per hour: 700 up to 1,000.

ENERGY STAR says the capacities are calculated based on an 8-foot ceiling. The chart starts at 100 square feet and has no row for a smaller room. Our reading: “150 up to 250” means 150 and above but under 250, so a room of exactly 250 square feet falls in the next band, 7,000.

Adjustments for sun, people and kitchens, with worked numbers

After the chart, ENERGY STAR lists four adjustments.

• Heavily shaded room: reduce the capacity by 10 percent.
• Very sunny room: increase it by 10 percent.
• More than two people regularly in the room: add 600 BTU per hour for each additional person.
• Unit used in a kitchen: add 4,000 BTU per hour.

Here is our arithmetic on four example rooms, applying one adjustment to the chart number for each:

• A 12 by 15 foot bedroom is 180 square feet, which is the 6,000 band. Heavy shade lowers that to 5,400.
• A 14 by 20 foot living room is 280 square feet, which is the 7,000 band. Very sunny raises that to 7,700.
• A 12 by 16 foot room is 192 square feet, which is the 6,000 band. If four people use it regularly, two extra people add 1,200, for 7,200.
• A 10 by 20 foot kitchen is 200 square feet, which is the 6,000 band. The kitchen adjustment makes that 10,000.

ENERGY STAR's page does not say how to combine two adjustments, such as a sunny kitchen. Our reading: start from the chart number, add or subtract each adjustment, and treat the total as a range to compare with the sizes a model line actually offers.

A maker's chart, and why “go up a size” can mislead

TCL, a television and appliance maker, publishes a window air conditioner sizing chart on its support page. It lists 5,000 BTU for 150 square feet, 6,000 for 250, 8,000 for 350, 10,000 for 450 and 12,000 for 550. The page does not say whether each area is a maximum or a midpoint. Our reading: they are maximums, because all five line up with the top of the matching ENERGY STAR band.

Our reading: a shopper who picks the nearest TCL row for a 400 square foot room could land on 8,000 or on 10,000. ENERGY STAR's band of 400 up to 450 square feet says 10,000.

Beyond floor area, TCL asks about direct sunlight and the number of windows. It also asks about people in the room, large appliances such as refrigerators or stoves in use, and ceilings taller than the standard 8 to 10 feet. If any of those apply, TCL says to consider going up to the next size on its chart.

ENERGY STAR warns the other way: it says cool, moist air from a unit that is too big makes the room feel damp and clammy. Our reading: the two sources pull in opposite directions, so going up a size should be a deliberate step for a named reason, not a habit.

TCL also says its higher-capacity units, marked with an asterisk from 18,000 BTU up, need 230 volts and do not use the standard 120 volt plugs found in homes. Our reading: a large unit can turn a sizing choice into an outlet question. Outlet and circuit work is for a licensed electrician, and this page gives no wiring steps.

Sizing for a humid Tampa Bay summer

The National Weather Service Tampa Bay Area office gives May 25 to October 10 as the rainy season for most of West Central Florida. The same office gives May 15 to October 15 for Southwest Florida. It ties that season to rising humidity, with dew points that stay above 70°F. Higher dew points mean wetter air, since the dew point is the temperature where vapor starts to condense. Our reading: in those months a window unit has a lot of moisture to remove, which makes ENERGY STAR's warning about oversizing more relevant here than in a dry climate.

ENERGY STAR's chart page lists no climate adjustment. Its tips say that on humid days a low fan speed removes more moisture, because slower air movement removes more moisture. Our reading: in Tampa Bay, a sunny room that needs the plus 10 percent is a better reason to size up than a general wish for extra power.

A window unit is a room-by-room answer. One ton is 12,000 BTU per hour, so the 12,000 row is a one-ton unit. For a whole house, see tons, load calculations and Florida code rules or why rules of thumb fall short in humid homes. If a room cannot take a window unit, what size mini-split you need sizes a ductless unit room by room.

Questions to ask before you buy

Questions to take to the store or to a licensed contractor:

1. What is the room's floor area in square feet, measured in feet?
2. Which chart band is that, and which of the four adjustments apply?
3. Is the ceiling taller than 8 feet?
4. If a maker's chart says to go up a size, which of its questions did I answer yes to?
5. Does the unit's label say 120 or 230 volts, and does the outlet match?
6. Does the window opening suit the unit I am considering?