Room AC BTU Calculator
Room air conditioner size in BTU/h from floor area by the ENERGY STAR sizing chart, adjusted for sun, people and a kitchen. Not a Manual J calculation. How it works
Use the Room AC BTU Calculator
About the Room AC BTU Calculator
A 300 sq ft room (20 × 15 ft) needs a room air conditioner of about 8,000 BTU/h, 0.67 tons, by the ENERGY STAR sizing chart. The room AC BTU calculator looks up the floor area in that chart, takes 10% off for a heavily shaded room, adds 10% for a very sunny one, 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h for a kitchen.
ENERGY STAR room air conditioner sizing chart
| Area to be cooled | Capacity needed |
|---|---|
| 100 up to 150 sq ft | 5,000 BTU/h |
| 150 up to 250 sq ft | 6,000 BTU/h |
| 250 up to 300 sq ft | 7,000 BTU/h |
| 300 up to 350 sq ft | 8,000 BTU/h |
| 350 up to 400 sq ft | 9,000 BTU/h |
| 400 up to 450 sq ft | 10,000 BTU/h |
| 450 up to 550 sq ft | 12,000 BTU/h |
| 550 up to 700 sq ft | 14,000 BTU/h |
| 700 up to 1,000 sq ft | 18,000 BTU/h |
| 1,000 up to 1,200 sq ft | 21,000 BTU/h |
| 1,200 up to 1,400 sq ft | 23,000 BTU/h |
| 1,400 up to 1,500 sq ft | 24,000 BTU/h |
| 1,500 up to 2,000 sq ft | 30,000 BTU/h |
For an 8 ft ceiling. The lower bound of each row is included, so 250 sq ft is 7,000 BTU/h. The ENERGY STAR chart has one more row, 2,000 up to 2,500 sq ft, which the calculator does not use: from 2,000 sq ft it asks you to get a load calculation from an installer.
Room air conditioner size for common rooms
| Room | Area | Normal sun | Heavily shaded | Very sunny | Tons (normal sun) |
|---|---|---|---|---|---|
| 10 × 12 ft | 120 sq ft | 5,000 | 4,500 | 5,500 | 0.42 |
| 12 × 12 ft | 144 sq ft | 5,000 | 4,500 | 5,500 | 0.42 |
| 12 × 15 ft | 180 sq ft | 6,000 | 5,400 | 6,600 | 0.50 |
| 15 × 20 ft | 300 sq ft | 8,000 | 7,200 | 8,800 | 0.67 |
| 20 × 20 ft | 400 sq ft | 10,000 | 9,000 | 11,000 | 0.83 |
| 20 × 25 ft | 500 sq ft | 12,000 | 10,800 | 13,200 | 1.00 |
| 25 × 25 ft | 625 sq ft | 14,000 | 12,600 | 15,400 | 1.17 |
| 30 × 30 ft | 900 sq ft | 18,000 | 16,200 | 19,800 | 1.50 |
| 30 × 40 ft | 1,200 sq ft | 23,000 | 20,700 | 25,300 | 1.92 |
| 40 × 40 ft | 1,600 sq ft | 30,000 | 27,000 | 33,000 | 2.50 |
BTU/h for two people, not a kitchen, with an 8 ft ceiling.
Frequently asked questions
- What size air conditioner do I need for a 12x12 room?
- 144 sq ft is in the 100 up to 150 sq ft row of the ENERGY STAR chart: 5,000 BTU/h. Heavily shaded it is 4,500 BTU/h and very sunny 5,500 BTU/h.
- How many BTU per square foot for a room air conditioner?
- The chart is not a fixed figure per square foot. The default 300 sq ft room works out to 26.7 BTU/h per sq ft, while a 500 sq ft room at 12,000 BTU/h is 24.0 BTU/h per sq ft. The calculator shows the figure for your room under the result.
- How do people and a kitchen change the size?
- Each person who regularly uses the room beyond two adds 600 BTU/h, and kitchen use adds 4,000 BTU/h. A very sunny 300 sq ft room with four people needs 8,000 + 800 + 1,200 = 10,000 BTU/h; the same room used as a kitchen with two people needs 12,000 BTU/h, 1.00 ton.
- Is this a Manual J calculation?
- No. An ACCA Manual J calculation works out the heat gain of the house from its insulation, windows, orientation, local climate and air leakage. The ENERGY STAR chart looks only at floor area, and its adjustments cover sun, people and a kitchen, so two rooms of the same size get the same figure however well they are built.
- What if my room is very large or has a high ceiling?
- Rooms under 100 sq ft or of 2,000 sq ft and more are outside the part of the chart the calculator uses, so it shows a message and suggests a load calculation instead of a size. A 40 × 40 ft room, 1,600 sq ft, is still in the chart at 30,000 BTU/h. The chart assumes an 8 ft ceiling; with a taller one the calculator warns that the figure may be low but does not adjust it.
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