A 3-ton air conditioner moves 36,000 BTU of heat per hour. The contractors' rule of thumb (400–600 sq ft per ton) would put it at about 1,200–1,800 sq ft, but that rule tends to oversize: in one sample of measured Manual J loads, homes averaged about 1,431 sq ft per ton, which would make it about 4,293 sq ft. A Manual J calculation is the real answer.
- Capacity
- 36,000BTU per hour
- Rule of thumb
- 1,200–1,800sq ft (tends to oversize)
- Manual J sample avg
- ~4,293sq ft
What a ton means
A ton of cooling is 12,000 BTU per hour, the heat needed to melt a ton of ice in a day. A 3-ton system is 36,000 BTU/hr, equal to about 10.6 kW of heat removed (not the electricity it uses).
Why square-foot rules mislead
Size with an ACCA Manual J load calculation. DOE Building Science Education: rules of thumb too often used and result in excessively oversized systems. Bailes: a Manual J result under 1,000 sq ft/ton is likely wrong. Show sq-ft/ton only as a rough range.
Questions people ask
How many square feet does a 3 ton AC cool?
A 3-ton air conditioner moves 36,000 BTU of heat per hour. The contractors' rule of thumb (400–600 sq ft per ton) would put it at about 1,200–1,800 sq ft , but that rule tends to oversize: in one sample of measured Manual J loads, homes averaged about 1,431 sq ft per ton, which would make it about 4,293 sq ft. A Manual J calculation is the real answer.
How many BTU is a 3 ton air conditioner?
36,000 BTU per hour (1 ton = 12,000 BTU/hr).
How is central air sized?
With an ACCA Manual J load calculation that accounts for insulation, windows, orientation, air leakage and climate. The DOE notes rules of thumb often lead to oversized systems.