What size air conditioner do I need for a 1,500 sq ft house? (tons by home size)
Read as one open floor, a 1,500 sq ft house is 30,000 BTU/h on the ENERGY STAR chart (its "1,500 up to 2,000" band), which is 2.50 tons, a 2.5-ton class. Read room by room, the same house is 7 room units that add up to 44,000 BTU/h, 3.67 tons, because the chart never gives a room less than 5,000 BTU/h. Both readings are below, for 1,000 to 3,000 sq ft houses and for a worked seven-room example, with what each one means.
1. What size air conditioner by house size, read as one open floor?
The ENERGY STAR chart (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart) is a room air conditioner chart, and its bands run to 2,500 sq ft, so a house up to that size can be read off it as if it were one open space: average sun, two people, 8 ft ceiling. Tons = BTU/h / 12,000; the class is the next half ton. Above 2,500 sq ft the calculator says so and stops.
| House (sq ft) | Chart band (sq ft) | BTU/h | Tons | kW | Class | Very sunny |
|---|---|---|---|---|---|---|
| 1,000 | 1,000 up to 1,200 | 21,000 | 1.75 | 6.15 | 2 tons | 23,100 |
| 1,200 | 1,200 up to 1,400 | 23,000 | 1.92 | 6.74 | 2 tons | 25,300 |
| 1,400 | 1,400 up to 1,500 | 24,000 | 2 | 7.03 | 2 tons | 26,400 |
| 1,500 | 1,500 up to 2,000 | 30,000 | 2.5 | 8.79 | 2.5 tons | 33,000 |
| 1,800 | 1,500 up to 2,000 | 30,000 | 2.5 | 8.79 | 2.5 tons | 33,000 |
| 2,000 | 2,000 up to 2,500 | 34,000 | 2.83 | 9.96 | 3 tons | 37,400 |
| 2,400 | 2,000 up to 2,500 | 34,000 | 2.83 | 9.96 | 3 tons | 37,400 |
| 2,500 | above 2,500 | room by room | — | — | — | — |
| 3,000 | above 2,500 | room by room | — | — | — | — |
1,500 sq ft is 30,000 BTU/h, 2.50 tons, the same figure for anything from 1,500 to just under 2,000 sq ft; 2,000 sq ft steps to 34,000 BTU/h. The AC BTU calculator gives this reading for any area and, in the Pro report, adds up the rooms as in table 2.
2. The same 1,500 sq ft house room by room
A single-storey house with the rooms that would get a unit: living room 16 x 20 ft, kitchen 12 x 16 ft, dining room 12 x 12 ft, main bedroom 14 x 16 ft, bedroom 2 12 x 12 ft, bedroom 3 11 x 12 ft, home office 10 x 12 ft. That is 1,276 sq ft of rooms; the other 224 sq ft are halls, bathrooms and closets, which get no unit. Each room is looked up on the chart with average sun and two people; the kitchen carries the chart's +4,000 BTU/h. This is the arithmetic of the Pro whole-home report.
| Room | Size (ft) | Area (sq ft) | Chart band | BTU/h | Tons |
|---|---|---|---|---|---|
| Living room | 16 x 20 | 320 | 300 up to 350 | 8,000 | 0.67 |
| Kitchen | 12 x 16 | 192 | 150 up to 250 | 10,000 | 0.83 |
| Dining room | 12 x 12 | 144 | 100 up to 150 | 5,000 | 0.42 |
| Main bedroom | 14 x 16 | 224 | 150 up to 250 | 6,000 | 0.5 |
| Bedroom 2 | 12 x 12 | 144 | 100 up to 150 | 5,000 | 0.42 |
| Bedroom 3 | 11 x 12 | 132 | 100 up to 150 | 5,000 | 0.42 |
| Home office | 10 x 12 | 120 | 100 up to 150 | 5,000 | 0.42 |
| Total of the room units | 1,276 | 44,000 | 3.67 (class 4) |
The kitchen alone is 10,000 BTU/h: 6,000 for its 192 sq ft plus 4,000 for cooking. The 4 rooms under 150 sq ft take 5,000 BTU/h each, the chart's floor, which is why the units add up to 44,000 BTU/h against 30,000 BTU/h for the whole floor as one space. Room sizes for the bedrooms are in the bedroom BTU guide.
3. Which reading do I use?
Room units (window, through-wall, portable, or one mini-split head per room): table 2, one figure per room, 7 units for this house. A central system or a single ducted unit: neither reading is the installer's figure. Table 1 says what the chart gives for the floor as a whole (30,000 BTU/h, 2.50 tons); table 2 says what the rooms need one at a time (44,000 BTU/h, 3.67 tons). A Manual J load calculation on the whole envelope, which counts windows, orientation, insulation and the local design temperature, is what a central system is bought on; the chart readings are the first estimate and the check on the quote.
With the chart's adjustments, the single-space reading for 1,500 sq ft moves from 27,000 BTU/h (heavily shaded) to 33,000 BTU/h (very sunny) and 38,200 BTU/h with four people and an open kitchen as well; the same adjustments per size are in the 1,000 sq ft guide. In kW, the whole-floor reading is 8.79 kW and the room units 12.90 kW.
Frequently asked questions
- What size air conditioner do I need for a 1,500 sq ft house?
- 30,000 BTU/h, 2.50 tons, if the 1,500 sq ft is one open space on the chart (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart); 33,000 BTU/h if it is very sunny. As separate rooms, each looked up on its own, the example house in table 2 comes to 44,000 BTU/h of room units, 3.67 tons, a 4-ton class on the Pro report. A central system is bought on an installer's Manual J, which sizes the whole envelope; the two chart readings are the first estimate and the check on the quote.
- What size air conditioner do I need for a 1,200 sq ft house?
- 23,000 BTU/h as one space, the "1,200 up to 1,400" band, 1.92 tons (a 2-ton class). Table 1 has 1,000 to 2,400 sq ft on the same reading.
- What size air conditioner do I need for a 2,000 sq ft house?
- 34,000 BTU/h as one space, the "2,000 up to 2,500" band, 2.83 tons (a 3-ton class); 1,800 sq ft is 30,000 BTU/h, 2.50 tons. The chart stops at 2,500 sq ft: a 2,500 or 3,000 sq ft house has no single-space reading and is sized room by room or by an installer.
- How many tons of AC per square foot?
- On the chart's single-space reading, 1.67 tons per 1,000 sq ft at 1,500 sq ft and 1.42 at 2,000 sq ft; the figure falls as the area grows because the chart's BTU per sq ft falls with size. Room by room it is higher: the example house is 2.87 tons per 1,000 sq ft of rooms.
- Why do the rooms add up to more than the whole floor?
- Because the chart's smallest figure is 5,000 BTU/h for any room under 150 sq ft. The 4 small rooms of the example (dining room, bedroom 2, bedroom 3, home office, 540 sq ft together) are 20,000 BTU/h as 4 units but 12,000 BTU/h as one open space of 540 sq ft. Room units are sized so each room cools on its own; a central system serves the rooms in turn.
- Is the room-by-room total the size of a central air conditioner?
- No: it is the size of the room units, and the Pro report labels it that way (3.67 tons, a 4-ton class for the example). A central system is sized by a Manual J load calculation on the whole house: windows, orientation, insulation, air leakage and the local design temperature. The chart gives the first estimate both ways; the installer's figure is the one equipment is bought on.
More guides
- How many BTU do I need per square foot? (room size chart)
The ENERGY STAR room size to BTU chart with its adjustments, heating BTU and tons by home size and climate zone, and m² to kW at three insulation levels.
- How many BTU do I need for a bedroom? (12x12 and other room sizes)
A 12 x 12 bedroom is 5,000 BTU/h on the ENERGY STAR chart. Eight bedroom sizes with the sun, people and ceiling adjustments, m² to kW, and the unit class for each.
- How many BTU do I need for 1,000 sq ft? (200 to 1,200 sq ft, cooling and heating)
1,000 sq ft is 21,000 BTU/h on the ENERGY STAR chart (1.75 tons) and 32,500-55,000 BTU/h to heat by zone. 200 to 1,200 sq ft, with the adjustments.
- What size radiator do I need? (BTU and watts by room size and type, UK)
BTU/h and watts for UK room sizes by type from the merchants' ft³ x factor rule, each adjustment, and the flat x4 rule. A 4 x 4 m living room: 7,500 BTU/h.
Last updated 2026-09-22. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.