A thousand square feet is a two-bedroom apartment, a 1950s ranch house, a full finished basement, a condo, or a single-wide manufactured home. The cooling load is 20,000 BTU/hr, 1.67 tons, which sits awkwardly between the 1.5-ton and 2-ton sizes that central air conditioners come in. The calculator rounds up to 24,000 BTU, and 2 tons is indeed the usual install.
Only a shaded, well-insulated 1,000 sq ft home (16,200) fits 1.5 tons, and a shaded one with average insulation (18,000) fits it with no margin. Every other row is 2 tons: very sunny (22,000), poor insulation (23,000), four people (21,200), a kitchen (24,000). Sunny plus poor (25,300), a 10 ft ceiling (25,000) and a hot climate with sun (24,200) reach 2.5 tons (30,000 BTU). So a 1,000 sq ft home spans a full ton depending on how it is built and where it sits, and the table is worth reading closely.
The common oversizing story at this size is the 3-ton quote. Thirty-six thousand BTU is 80 percent over the base load and about 30 percent over even the hot, sunny, poorly insulated case. A 3-ton unit on a 1,000 sq ft ranch will run in short bursts, the coil never gets cold enough for long enough to dehumidify, and the house feels clammy at 74 degrees. Two tons, or 2.5 in a hot climate, is the honest range.
Ductless works well at 1,000 sq ft if the plan has three or four rooms: a 24,000 to 30,000 BTU outdoor unit with a 12,000 BTU head in the living and kitchen area and 6,000 to 9,000 BTU heads in each bedroom. A single 24,000 BTU head in the living room will leave the bedrooms warm.
Heating 1,000 sq ft takes 30,000 BTU/hr in a hot climate, 40,000 in a moderate one (11.7 kW) and 55,000 in a cold one (16.1 kW). Forty thousand is the smallest furnace most brands make, and it fits the moderate case exactly; a cold climate wants 60,000. With good insulation the cold-climate figure drops to 46,800, and with poor insulation it rises to 66,000. A 2-ton cold-climate heat pump with electric backup covers a 1,000 sq ft home almost anywhere in the lower 48.
Example: a 1,000 sq ft ranch with a kitchen, three people, west-facing living room windows, average insulation, hot climate. 1,000 × 20 = 20,000, times 1.10 for sun and 1.10 for the climate, is 24,200, plus 600 for the third person and 4,000 for the kitchen, is 28,800 BTU/hr. That is 2.5 tons. Move the same house to a moderate climate with shade and good insulation and it is 16,200 + 4,600 = 20,800, a 2-ton system with margin. Same footage, half a ton apart.
Cooling BTU for 1,000 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 | 20,700buy 24,000 BTU | 18,000buy 18,000 BTU | 16,200buy 18,000 BTU |
| Average | 23,000buy 24,000 BTU | 20,000buy 24,000 BTU | 18,000buy 18,000 BTU |
| Very sunny | 25,300buy 30,000 BTU | 22,000buy 24,000 BTU | 19,800buy 24,000 BTU |
Common adjustments for a 1,000 sq ft room
| Scenario | Cooling BTU/hr | Unit to buy |
|---|---|---|
| Average (baseline) | 20,000 | 24,000 BTU |
| 4 people instead of 2 | 21,200 | 24,000 BTU |
| 10 ft ceiling | 25,000 | 30,000 BTU |
| Kitchen in the space | 24,000 | 24,000 BTU |
| Hot climate, very sunny | 24,200 | 30,000 BTU |
Heating BTU for 1,000 sq ft by climate and insulation
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 36,00010.6 kW | 30,0008.8 kW | 25,5007.5 kW |
| moderate | 48,00014.1 kW | 40,00011.7 kW | 34,00010.0 kW |
| cold | 66,00019.3 kW | 55,00016.1 kW | 46,80013.7 kW |
1,000 sq ft sizing questions
What size air conditioner do I need for a 1,000 sq ft room?
About 20,000 BTU/hr in average conditions (1.7 tons), so a 24,000 BTU unit. The table above covers sunnier and worse-insulated rooms.
Do I need 1.5, 2 or 2.5 tons for 1,000 sq ft?
Two tons in most cases. The floor area is 20,000 BTU/hr, and a kitchen, extra people, sun or poor insulation take it to 21,000 to 24,000. Only a shaded, well-insulated home (16,200) fits 1.5 tons, and only a hot, sunny or tall-ceilinged home (24,200 to 25,300) needs 2.5 tons.
Is a 3-ton AC too big for 1,000 sq ft?
Yes. 36,000 BTU is 80 percent above the 20,000 BTU/hr base load and well above even the hot, sunny, poorly insulated case (27,800). It will short-cycle and leave the house humid. Stay at 2 tons, or 2.5 in a hot climate.
What size furnace for a 1,000 sq ft house?
About 40,000 BTU/hr in a moderate climate with average insulation and 55,000 in a cold one, so a 40,000 BTU furnace in most of the country and a 60,000 BTU furnace in the north. With good insulation the cold-climate figure is 46,800.