Six hundred square feet is the living zone of a one-bedroom apartment, a 24 by 25 garage, a large finished basement, or a small open-plan cottage. It is also one ton exactly: 600 × 20 = 12,000 BTU/hr. A 12,000 BTU air conditioner is the nominal answer and, like every 'exact' match, it only works in an average or better room.
Push anything and you are at 14,000 BTU: very sunny (13,200), poor insulation (13,800), four people (13,200). Push two things and you are at 18,000 BTU: sunny plus poor is 15,200, a 10 ft ceiling is 15,000, a kitchen is 16,000, hot climate plus sun is 14,500. Meanwhile a shaded, well-insulated 600 sq ft room is 9,700 and a 10,000 BTU unit does it. The spread from 10,000 to 18,000 is why the honest answer at this size depends more on the row you pick in the table than on the square footage.
600 sq ft is also where a single unit starts losing to two. A one-bedroom apartment with a 350 sq ft living area and a 250 sq ft bedroom does better with an 8,000 BTU unit in the living room and a 6,000 in the bedroom than with one 14,000 in the living room, because the bedroom door closes at night and a window unit cannot cool through a wall. The two-unit approach also runs on two ordinary outlets.
For a mini-split the choice is between a 12,000 and an 18,000 BTU head. Take the 12k for a shaded or well-insulated space and the 18k for a sunny or poorly insulated one; inverters modulate down, so the 18k will not short-cycle on a mild day the way an oversized window unit does. A 24,000 BTU head in 600 sq ft is oversized even for the worst row.
Heating 600 sq ft with average insulation runs 18,000 BTU/hr in a hot climate, 24,000 in a moderate one (7.0 kW) and 33,000 in a cold one (9.7 kW). A poorly insulated garage in a cold climate is 39,600, a 40,000 BTU gas unit heater or a 12 kW electric unit heater. For a finished basement in the north, an 18,000 BTU heat pump mini-split with a couple of baseboard heaters as backup is the common and sensible setup.
Example: a 24 by 25 finished basement in a cold-climate state, two people, good insulation, no direct sun. Cooling: 600 × 20 = 12,000, times 0.90 for shade and 0.90 for the cold climate, is 9,700 BTU/hr, so a 10,000 BTU unit. Heating the same room: 600 × 55 = 33,000, times 0.85 for good insulation, is 28,100 BTU/hr, a 30,000 BTU heater or about 8 kW of electric heat.
Cooling BTU for 600 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 | 12,400buy 14,000 BTU | 10,800buy 12,000 BTU | 9,700buy 10,000 BTU |
| Average | 13,800buy 14,000 BTU | 12,000buy 12,000 BTU | 10,800buy 12,000 BTU |
| Very sunny | 15,200buy 18,000 BTU | 13,200buy 14,000 BTU | 11,900buy 12,000 BTU |
Common adjustments for a 600 sq ft room
| Scenario | Cooling BTU/hr | Unit to buy |
|---|---|---|
| Average (baseline) | 12,000 | 12,000 BTU |
| 4 people instead of 2 | 13,200 | 14,000 BTU |
| 10 ft ceiling | 15,000 | 18,000 BTU |
| Kitchen in the space | 16,000 | 18,000 BTU |
| Hot climate, very sunny | 14,500 | 18,000 BTU |
Heating BTU for 600 sq ft by climate and insulation
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 21,6006.3 kW | 18,0005.3 kW | 15,3004.5 kW |
| moderate | 28,8008.4 kW | 24,0007.0 kW | 20,4006.0 kW |
| cold | 39,60011.6 kW | 33,0009.7 kW | 28,1008.2 kW |
600 sq ft sizing questions
What size air conditioner do I need for a 600 sq ft room?
About 12,000 BTU/hr in average conditions (1.0 tons), so a 12,000 BTU unit. The table above covers sunnier and worse-insulated rooms.
Is 12,000 BTU enough for 600 sq ft?
Only in an average or shaded room; 600 sq ft is exactly 12,000 BTU/hr, so there is no margin. A very sunny or poorly insulated room needs 13,200 to 15,200 BTU/hr, which is a 14,000 or 18,000 BTU unit.
Should I use one AC or two for a 600 sq ft apartment?
Two, if it has a separate bedroom. An 8,000 BTU unit in a 350 sq ft living room and a 6,000 BTU unit in a 250 sq ft bedroom cool both rooms with the door closed; one 14,000 BTU unit in the living room cannot reach the bedroom.
How many BTU to heat 600 sq ft?
About 24,000 BTU/hr in a moderate climate with average insulation (7 kW), and 33,000 BTU/hr in a cold climate. With good insulation the cold-climate figure drops to 28,100, which an 18,000 BTU heat pump plus a little backup heat can handle.