Seven hundred square feet is a whole small one-bedroom apartment, an open-concept living, kitchen and dining area, a three-car garage (30 by 24 is 720), or a pole-barn workshop. The load is 14,000 BTU/hr, and this is the first size where the shopping answer is almost never a window unit.
The numbers explain why. 14,000 BTU is the exact load, so a 14,000 BTU unit has no margin. Very sunny is 15,400, poor insulation is 16,100, four people is 15,200, a 10 ft ceiling is 17,500, a kitchen is 18,000: all of those are an 18,000 BTU unit, which in window form is heavy and usually needs a 230 V circuit. A hot climate with sun and poor insulation is 19,500, a 24,000 BTU unit, and that size does not exist as a window air conditioner in any practical sense.
The bigger problem is distribution. A 700 sq ft apartment has walls and doors, and one air conditioner, however large, cools the room it sits in and leaks a little into the next one. People try it with a single 18,000 BTU unit in the living room, leave the bedroom door open all night, and still sleep in a 78 degree room. At this size you either zone with two or three window units or you install a mini-split: an 18,000 BTU single-zone head for a truly open plan, or a two-zone system with a 12,000 BTU head in the living area and a 6,000 or 9,000 BTU head in the bedroom.
Heating 700 sq ft takes 21,000 BTU/hr in a hot climate, 28,000 in a moderate one (8.2 kW) and 38,500 in a cold one (11.3 kW). That is more than electric baseboards on one or two circuits can deliver; a 40,000 BTU gas furnace, which is the smallest most brands make, matches the cold case, and a 24,000 BTU heat pump with electric backup strips covers the moderate one. A three-car garage with poor insulation in a cold climate is 46,200 BTU/hr, a 45,000 to 50,000 BTU unit heater.
Example: a 700 sq ft top-floor one-bedroom with an open kitchen, two people, average sun, poor insulation under the roof, moderate climate. As one zone: 700 × 20 = 14,000, times 1.15 for insulation is 16,100, plus 4,000 for the kitchen is 20,100 BTU/hr, a 24,000 BTU mini-split. As two zones: the 500 sq ft living and kitchen area is 10,000 × 1.15 + 4,000 = 15,500 (an 18,000 BTU head) and the 200 sq ft bedroom is 4,000 × 1.15 = 4,600 (a 6,000 BTU head or a 5,000 BTU window unit). The two-zone version costs more up front and is the one the tenant will be happier with.
Cooling BTU for 700 sq ft by sun exposure and insulation
Two occupants, 8 ft ceiling, moderate climate. Each cell shows BTU/hr needed and the unit size to buy.
| Sun exposure | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| Heavily shaded | 14,500buy 18,000 BTU | 12,600buy 14,000 BTU | 11,300buy 12,000 BTU |
| Average | 16,100buy 18,000 BTU | 14,000buy 14,000 BTU | 12,600buy 14,000 BTU |
| Very sunny | 17,700buy 18,000 BTU | 15,400buy 18,000 BTU | 13,900buy 14,000 BTU |
Common adjustments for a 700 sq ft room
| Scenario | Cooling BTU/hr | Unit to buy |
|---|---|---|
| Average (baseline) | 14,000 | 14,000 BTU |
| 4 people instead of 2 | 15,200 | 18,000 BTU |
| 10 ft ceiling | 17,500 | 18,000 BTU |
| Kitchen in the space | 18,000 | 18,000 BTU |
| Hot climate, very sunny | 16,900 | 18,000 BTU |
Heating BTU for 700 sq ft by climate and insulation
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 25,2007.4 kW | 21,0006.2 kW | 17,9005.2 kW |
| moderate | 33,6009.8 kW | 28,0008.2 kW | 23,8007.0 kW |
| cold | 46,20013.5 kW | 38,50011.3 kW | 32,7009.6 kW |
700 sq ft sizing questions
What size air conditioner do I need for a 700 sq ft room?
About 14,000 BTU/hr in average conditions (1.2 tons), so a 14,000 BTU unit. The table above covers sunnier and worse-insulated rooms.
Can one window AC cool a 700 sq ft apartment?
Not if it has a separate bedroom. The total load is 14,000 to 18,000 BTU/hr, but a single unit only cools the room it is in. Use an 18,000 BTU unit for a truly open 700 sq ft plan, or two units (or a two-zone mini-split) for an apartment with a bedroom.
What size mini-split for 700 sq ft?
An 18,000 BTU single-zone head for an open floor plan in average conditions (14,000 BTU/hr load, 15,400 to 16,100 with sun or poor insulation). With a kitchen or in a hot, sunny spot the load reaches 18,000 to 19,500 BTU/hr, where a 24,000 BTU head or a two-zone 12,000 + 9,000 system fits better.
How many BTU to heat 700 sq ft?
About 28,000 BTU/hr in a moderate climate with average insulation (8.2 kW) and 38,500 in a cold one. That is a 40,000 BTU furnace, a 2-ton heat pump with backup strips, or, for a three-car garage, a 45,000 BTU unit heater.