How many BTU do I need for 1,000 sq ft? (200 to 1,200 sq ft, cooling and heating)
To cool 1,000 sq ft as one open space you need 21,000 BTU/h on the ENERGY STAR room air conditioner chart (its "1,000 up to 1,200" band), which is 1.75 tons or 6.15 kW; a very sunny space is 23,100 BTU/h. To heat a 1,000 sq ft home the published climate-zone rule gives 32,500 BTU/h in zone 1 (hot) up to 55,000 BTU/h in zone 5 (cold) with average insulation. The tables below give every size from 200 to 1,200 sq ft, the chart's adjustments on 1,000 sq ft, and the heating figure in each zone.
1. How many BTU for 200 to 1,200 sq ft?
Each size looked up on the ENERGY STAR chart (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart) as one open space with average sun, two people and an 8 ft ceiling, then the chart's heavily shaded (x0.9) and very sunny (x1.1) adjustments. Tons = BTU/h / 12,000; kW = BTU/h / 3,412.
| Area (sq ft) | Chart band (sq ft) | BTU/h | Tons | kW | Heavily shaded | Very sunny |
|---|---|---|---|---|---|---|
| 200 | 150 up to 250 | 6,000 | 0.5 | 1.76 | 5,400 | 6,600 |
| 300 | 300 up to 350 | 8,000 | 0.67 | 2.34 | 7,200 | 8,800 |
| 400 | 400 up to 450 | 10,000 | 0.83 | 2.93 | 9,000 | 11,000 |
| 500 | 450 up to 550 | 12,000 | 1 | 3.52 | 10,800 | 13,200 |
| 600 | 550 up to 700 | 14,000 | 1.17 | 4.1 | 12,600 | 15,400 |
| 700 | 700 up to 1,000 | 18,000 | 1.5 | 5.28 | 16,200 | 19,800 |
| 800 | 700 up to 1,000 | 18,000 | 1.5 | 5.28 | 16,200 | 19,800 |
| 900 | 700 up to 1,000 | 18,000 | 1.5 | 5.28 | 16,200 | 19,800 |
| 1,000 | 1,000 up to 1,200 | 21,000 | 1.75 | 6.15 | 18,900 | 23,100 |
| 1,200 | 1,200 up to 1,400 | 23,000 | 1.92 | 6.74 | 20,700 | 25,300 |
700, 800 and 900 sq ft share one figure, 18,000 BTU/h, because the chart has a single "700 up to 1,000" band; 1,000 sq ft steps up to 21,000 BTU/h and 1,200 to 23,000 BTU/h. The AC BTU calculator looks up any area, in sq ft or m², and adds people, kitchen and ceiling height.
2. 1,000 sq ft with the chart's adjustments
The same 1,000 sq ft space with each adjustment on its own, then the three that add up: very sunny x1.1, 600 BTU/h per person beyond two, +4,000 BTU/h for a kitchen (ENERGY STAR, Room Air Conditioners, sizing chart notes). The 10 ft ceiling row scales the chart figure by height / 8 ft, our assumption, not the chart's (BTUtally assumption, not in the chart). The last column is the next chart capacity at or above the figure.
| Case | BTU/h | Tons | kW | Chart capacity |
|---|---|---|---|---|
| As charted (average sun, two people, 8 ft ceiling) | 21,000 | 1.75 | 6.15 | 21,000 BTU |
| Heavily shaded | 18,900 | 1.58 | 5.54 | 21,000 BTU |
| Very sunny | 23,100 | 1.93 | 6.77 | 24,000 BTU |
| Four people | 22,200 | 1.85 | 6.51 | 23,000 BTU |
| Open plan with the kitchen | 25,000 | 2.08 | 7.33 | 30,000 BTU |
| 10 ft ceiling | 26,250 | 2.19 | 7.69 | 30,000 BTU |
| Very sunny, four people, kitchen | 28,300 | 2.36 | 8.29 | 30,000 BTU |
A 10 ft ceiling adds 25 percent: 26,300 BTU/h instead of 21,000 BTU/h. Sunny, four people and an open kitchen together reach 28,300 BTU/h, so the next chart capacity is 30,000 BTU instead of 21,000 BTU. Whether that is one large unit or two smaller ones is a question of doorways; the 1,500 sq ft house guide shows what happens when rooms are added up.
3. How many BTU to heat 1,000 sq ft, by climate zone
Heating uses a different published rule (HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor): Zone 1 30-35, Zone 2 35-40, Zone 3 40-45, Zone 4 45-50, Zone 5 50-60 BTU per hour per sq ft, times 1,000 sq ft, times the insulation factor (poor 1.1, good 0.9). The midpoint is the figure; the furnace class rounds it up to the next 10,000 BTU/h and the heat pump class to the next half ton.
| Climate zone | Range, average (BTU/h) | poor: BTU/h | average: BTU/h | good: BTU/h | Furnace (average) | Heat pump (average) |
|---|---|---|---|---|---|---|
| Zone 1 | 30,000-35,000 BTU/h | 35,750 | 32,500 | 29,250 | 40,000 BTU/h | 3 tons |
| Zone 2 | 35,000-40,000 BTU/h | 41,250 | 37,500 | 33,750 | 40,000 BTU/h | 3.5 tons |
| Zone 3 | 40,000-45,000 BTU/h | 46,750 | 42,500 | 38,250 | 50,000 BTU/h | 4 tons |
| Zone 4 | 45,000-50,000 BTU/h | 52,250 | 47,500 | 42,750 | 50,000 BTU/h | 4 tons |
| Zone 5 | 50,000-60,000 BTU/h | 60,500 | 55,000 | 49,500 | 60,000 BTU/h | 5 tons |
In zone 4 with average insulation, 1,000 sq ft is 47,500 BTU/h (13.92 kW), a 50,000 BTU/h furnace class or a 4 ton heat pump class; with poor insulation, 52,300 BTU/h. The heat pump size calculator sets the zone from your state, and the BTU per square foot guide has 1,000 to 3,000 sq ft in every zone. Both rules are published shortcuts for a first estimate; a Manual J calculation replaces them.
Frequently asked questions
- How many BTU do I need for 1,000 sq ft?
- 21,000 BTU/h to cool it as a single space (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart: "1,000 up to 1,200" sq ft), 1.75 tons. That is the chart's figure for an open 1,000 sq ft floor with average sun and two people; 23,100 BTU/h if it is very sunny, 25,000 BTU/h if the kitchen is part of the space. Heating is a different rule: 47,500 BTU/h in zone 4 (table 3).
- How many BTU do I need for 800 sq ft?
- 18,000 BTU/h: 700, 800 and 900 sq ft all fall in the chart's "700 up to 1,000" band (1.50 tons). Very sunny, 19,800 BTU/h; heavily shaded, 16,200 BTU/h.
- How many BTU do I need for 500 sq ft?
- 12,000 BTU/h, the "450 up to 550" band, 1.00 tons or 3.52 kW. 600 sq ft moves up to 14,000 BTU/h ("550 up to 700"); 400 sq ft is 10,000 BTU/h. Table 1 has every hundred from 200 to 1,200 sq ft.
- Is 1,000 sq ft one air conditioner or two?
- The chart gives 21,000 BTU/h for one open 1,000 sq ft space, but two 500 sq ft rooms with a wall between them are two units of 12,000 BTU/h, 24,000 BTU/h in all: each room is looked up on its own. Doors and walls decide, not the total. For a whole house, see the 1,500 sq ft house guide, which adds the rooms up.
- How many BTU does it take to heat 1,000 sq ft?
- 45,000-50,000 BTU/h in zone 4 with average insulation, 47,500 BTU/h at the midpoint, a furnace of 50,000 BTU/h output or a heat pump of 4 tons (HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor). Zone 1 is 32,500 BTU/h; zone 5, 55,000 BTU/h. Table 3 has every zone at three insulation levels.
- What is 1,000 sq ft in square metres and kW?
- 92.9 m². Cooling it as one space is 6.15 kW (21,000 BTU/h / 3,412); heating it in zone 4 is 13.92 kW. A UK home of that size uses the W/m² rule in the boiler calculator instead of the US zones.
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.
- What size air conditioner do I need for a 1,500 sq ft house? (tons by home size)
The chart reads 1,500 sq ft as 30,000 BTU/h (2.5 tons); room by room the units add to 44,000. Both readings, 1,000-3,000 sq ft, and a seven-room example.
- 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.