Five hundred fifty square feet is a big studio, a 22 by 25 open living and dining room, a 24 by 24 two-car garage with a workbench (576), or the main floor of a small cottage. The load is 11,000 BTU/hr, and a 12,000 BTU unit covers the average version of the room with 1,000 BTU in hand.
This is the upper edge of what a single window unit does well. Very sunny (12,100), poor insulation (12,600), four people (12,200) and sunny plus poor (13,900) all call for a 14,000 BTU unit, and a kitchen in the space (15,000) or a hot sunny room with poor insulation (15,300) means 18,000 BTU. Window units at 14,000 BTU and up weigh over 100 pounds, and many at 18,000 need a 230 V circuit, so the practical path above 12,000 is usually a mini-split or two smaller units.
The trap at 550 sq ft is the portable air conditioner. A box labelled 14,000 BTU sounds like a fit, but that is the ASHRAE figure; the same single-hose unit is rated around 9,500 BTU SACC once you count the hot air it pulls back in through the walls. That is 1,500 BTU short of the base load before the sun comes out. If it has to be a portable, get a dual-hose model and accept that it will struggle on the hottest afternoons.
A 12,000 BTU mini-split fits the average room; an 18,000 BTU head fits the sunny or kitchen version and, being an inverter, turns down to 6,000 or so when the room is mild. Splitting the area into two window units, an 8,000 in the living end and a 6,000 or 8,000 in the dining or kitchen end, is the budget answer and gives more even temperatures than one big unit.
Heating 550 sq ft needs 16,500 BTU/hr in a hot climate, 22,000 in a moderate one (6.5 kW) and 30,300 in a cold one (8.9 kW). A garage with poor insulation in a cold climate is 36,300 BTU/hr, which is a 40,000 BTU gas unit heater; 10 kW of electric heat (34,000 BTU/hr) falls just short.
Example: a 22 by 25 living and dining room open to a kitchen, three people, average sun and insulation, moderate climate. 550 × 20 = 11,000, plus 600 for the third person and 4,000 for the kitchen, is 15,600 BTU/hr. One unit means 18,000 BTU. Split as a 350 sq ft living end (7,000, an 8,000 BTU unit) and a 200 sq ft dining and kitchen end (4,000 plus 4,000, an 8,000 BTU unit), two 8,000 BTU window units do the same job more evenly and on two ordinary outlets.
Cooling BTU for 550 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 | 11,400buy 12,000 BTU | 9,900buy 10,000 BTU | 8,900buy 10,000 BTU |
| Average | 12,600buy 14,000 BTU | 11,000buy 12,000 BTU | 9,900buy 10,000 BTU |
| Very sunny | 13,900buy 14,000 BTU | 12,100buy 14,000 BTU | 10,900buy 12,000 BTU |
Common adjustments for a 550 sq ft room
| Scenario | Cooling BTU/hr | Unit to buy |
|---|---|---|
| Average (baseline) | 11,000 | 12,000 BTU |
| 4 people instead of 2 | 12,200 | 14,000 BTU |
| 10 ft ceiling | 13,800 | 14,000 BTU |
| Kitchen in the space | 15,000 | 18,000 BTU |
| Hot climate, very sunny | 13,300 | 14,000 BTU |
Heating BTU for 550 sq ft by climate and insulation
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 19,8005.8 kW | 16,5004.8 kW | 14,0004.1 kW |
| moderate | 26,4007.7 kW | 22,0006.4 kW | 18,7005.5 kW |
| cold | 36,30010.6 kW | 30,3008.9 kW | 25,7007.5 kW |
550 sq ft sizing questions
What size air conditioner do I need for a 550 sq ft room?
About 11,000 BTU/hr in average conditions (0.92 tons), so a 12,000 BTU unit. The table above covers sunnier and worse-insulated rooms.
Is 12,000 BTU enough for 550 sq ft?
For an average or shaded room, yes: the load is 11,000 BTU/hr, or 9,900 with shade. A very sunny or poorly insulated 550 sq ft room needs 12,100 to 13,900 BTU/hr, which is a 14,000 BTU unit, and adding a kitchen takes it to 18,000 BTU.
Will a 14,000 BTU portable AC cool 550 sq ft?
Probably not well. A 14,000 BTU ASHRAE single-hose portable delivers roughly 9,500 BTU SACC, below the 11,000 BTU/hr the room needs. A dual-hose model does better, but a 12,000 BTU window unit or mini-split is the more reliable choice.
How many BTU to heat 550 sq ft?
About 22,000 BTU/hr in a moderate climate with average insulation (6.5 kW) and 30,300 in a cold climate. An uninsulated 550 sq ft garage in a cold climate needs 36,300 BTU/hr, a 40,000 BTU gas unit heater.