Fifteen hundred square feet is the typical three-bedroom, two-bath house, a large open main floor with a kitchen, or a whole small two-story home. The cooling load is 30,000 BTU/hr, exactly 2.5 tons, and 2.5 tons is the most common residential central air size in the US for precisely this reason. It is also, like every exact match, a size with no margin.
Most 1,500 sq ft homes therefore end up at 3 tons (36,000 BTU). Very sunny is 33,000, poor insulation 34,500, a kitchen 34,000, four people 31,200: all 3 tons. Sunny with poor insulation (38,000), a 10 ft ceiling (37,500) or a hot climate with sun (36,300) come to 3.5 tons, which the calculator displays as 48,000 BTU because it does not carry a 42,000 class; a contractor would quote 3.5. A shaded, well-insulated house is 24,300, and 2.5 tons has real margin there.
The rule of thumb runs high for newer construction. A 1,500 sq ft house built to a 2015 or later energy code, with a sealed attic and low-E windows, often comes back from a Manual J at 2 tons, half a ton to a full ton below the table. The rule of thumb still protects you from the other direction: a quote for 4 tons on 1,500 sq ft is 60 percent over the base load and should be questioned unless the house is a glass box in Phoenix.
Heating 1,500 sq ft with average insulation is 45,000 BTU/hr in a hot climate, 60,000 in a moderate one (17.6 kW) and 82,500 in a cold one (24.2 kW). Sixty thousand is a common furnace size and fits the moderate case; 80,000 is the most common furnace sold and fits the cold case with average insulation, while the cold-poor case (99,000) needs a 100,000 model. Remember furnaces are rated on input; an 80,000 BTU furnace at 96 percent efficiency delivers about 76,800 BTU/hr, so compare that figure to the table. Good insulation in a cold climate drops the load to 70,100.
Example: a 1,500 sq ft house in a hot climate with a kitchen, four people, sunny exposure and average insulation. 1,500 × 20 = 30,000, times 1.10 for sun and 1.10 for the climate, is 36,300, plus 1,200 for the people and 4,000 for the kitchen, is 41,500 BTU/hr. That is a 3.5-ton system. The same house in a moderate climate with shade and good insulation is 24,300 + 5,200 = 29,500, a 2.5-ton system. A full ton separates the two, and both are 1,500 sq ft.
Cooling BTU for 1,500 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 | 31,000buy 36,000 BTU | 27,000buy 30,000 BTU | 24,300buy 30,000 BTU |
| Average | 34,500buy 36,000 BTU | 30,000buy 30,000 BTU | 27,000buy 30,000 BTU |
| Very sunny | 38,000buy 48,000 BTU | 33,000buy 36,000 BTU | 29,700buy 30,000 BTU |
Common adjustments for a 1,500 sq ft room
| Scenario | Cooling BTU/hr | Unit to buy |
|---|---|---|
| Average (baseline) | 30,000 | 30,000 BTU |
| 4 people instead of 2 | 31,200 | 36,000 BTU |
| 10 ft ceiling | 37,500 | 48,000 BTU |
| Kitchen in the space | 34,000 | 36,000 BTU |
| Hot climate, very sunny | 36,300 | 48,000 BTU |
Heating BTU for 1,500 sq ft by climate and insulation
| Climate | Poor insulation | Average insulation | Good insulation |
|---|---|---|---|
| hot | 54,00015.8 kW | 45,00013.2 kW | 38,30011.2 kW |
| moderate | 72,00021.1 kW | 60,00017.6 kW | 51,00014.9 kW |
| cold | 99,00029.0 kW | 82,50024.2 kW | 70,10020.5 kW |
1,500 sq ft sizing questions
What size air conditioner do I need for a 1,500 sq ft room?
About 30,000 BTU/hr in average conditions (2.5 tons), so a 30,000 BTU unit. The table above covers sunnier and worse-insulated rooms.
Do I need 2.5 or 3 tons for 1,500 sq ft?
The floor area alone is exactly 30,000 BTU/hr (2.5 tons). Add a kitchen, sun, poor insulation or extra people and the load reaches 31,200 to 34,500 BTU/hr, which is 3 tons. A shaded, well-insulated 1,500 sq ft house (24,300) fits 2.5 tons comfortably.
Is 4 tons too much for 1,500 sq ft?
Almost always. Even a hot, sunny, poorly insulated 1,500 sq ft house comes to about 41,700 BTU/hr, which is 3.5 tons. Four tons (48,000 BTU) is 60 percent over the base load and will short-cycle in a normal house.
What size furnace for a 1,500 sq ft house?
About 60,000 BTU/hr in a moderate climate with average insulation and 82,500 in a cold one. That is a 60,000 BTU furnace in most of the country and an 80,000 in the north (100,000 if the house is poorly insulated). Compare the furnace's output rating, not its input, to these figures.