Room size bands
The area is matched to the first band whose upper bound is at least that big. A 350 square foot room uses 8,000 BTU per hour. A 351 square foot room uses 9,000. The result is then adjusted and rounded to the nearest 100 BTU per hour.
| Room area | BTU per hour |
|---|---|
| Up to 150 sq ft | 5,000 |
| Up to 250 sq ft | 6,000 |
| Up to 300 sq ft | 7,000 |
| Up to 350 sq ft | 8,000 |
| Up to 400 sq ft | 9,000 |
| Up to 450 sq ft | 10,000 |
| Up to 550 sq ft | 12,000 |
| Up to 700 sq ft | 14,000 |
| Up to 1,000 sq ft | 18,000 |
| Up to 1,200 sq ft | 21,000 |
| Up to 1,400 sq ft | 23,000 |
| Up to 1,500 sq ft | 24,000 |
| Up to 2,000 sq ft | 30,000 |
| Up to 2,500 sq ft | 34,000 |
Worked example
A sunny 350 square foot kitchen used by four people: start at 8,000, add 10 percent for sun (8,800), add 600 x 2 for the extra people (10,000), then add 4,000 for the kitchen. The recommendation is 14,000 BTU per hour.
Ceiling height, insulation, and climate are not in this table. If the room is tall, poorly insulated, or you are sizing central equipment, use Manual J instead of a window-unit chart.
Frequently asked questions
How many BTU do I need for a 500 square foot room?
500 square feet falls in the up-to-550 band, which is 12,000 BTU per hour before adjustments. A very sunny room adds 10 percent. Each regular occupant past two adds 600 BTU per hour. A kitchen adds 4,000.
How many BTU does a 350 square foot room need?
Up to 350 square feet maps to 8,000 BTU per hour on this table when the room has normal sun, two people, and is not a kitchen. At exactly 350 the calculator uses 8,000, because each band includes its upper bound.
What if the room is larger than 2,500 square feet?
Stop using a room-unit table. A house or a large open room needs a Manual J load calculation from an HVAC contractor. The calculator says so instead of inventing a BTU number.
Does a bigger air conditioner dehumidify better?
No. An oversized unit cools the air and shuts off before it has pulled out much moisture, so the room feels cold and clammy. Match the table, then apply only the adjustments that fit the room.