AC size for a 1,800 sq ft room
36,000 BTU
for a 1,800 sq ft room (3.0 tons) · about 3,000 W at EER 12
Adjust for the room
| Condition | BTU/h |
|---|---|
| Normal room | 36,000 |
| Very sunny (+10%) | 39,600 |
| Shaded (−10%) | 32,400 |
| Kitchen (+4,000) | 40,000 |
| Each extra person over 2 (+600) | +600 |
Rule of thumb: 20 BTU per sq ft with 8 ft ceilings (ENERGY STAR sizing guidance).
Monthly running cost at $0.17/kWh
| Use | Energy | Cost |
|---|---|---|
| 4 h/day | 360 kWh | $61 |
| 8 h/day | 720 kWh | $122 |
| 12 h/day | 1,080 kWh | $184 |
FAQ
What size AC for 1,800 square feet?
About 36,000 BTU (3.0 tons); add 10% for a sunny room and 4,000 BTU for a kitchen.
How much does it cost to run a 36,000 BTU AC?
At roughly 3,000 W, 8 hours a day for a month uses 720 kWh, about $122 at $0.17/kWh.