# Air conditioner BTU calculator

> Air conditioner size for a room in BTU/h, tons and kW from floor area, ceiling height, insulation, sun and occupants, beside the Energy Star chart.

Интерактивная версия: https://www.calcopenly.com/ru/construction/btu-calculator
Тема: Калькуляторы строительства и дома

The cooling load starts at 20 BTU/h per square foot for an 8 ft ceiling, scales with ceiling height and an insulation factor, then takes Energy Star's room air conditioner adjustments: 10% less for a heavily shaded room, 10% more for a very sunny one, 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h for a kitchen. The load is also given in tons (12,000 BTU/h each) and kW, with the next common unit size.

A 300 ft² room with an 8 ft ceiling and average conditions comes to 6,000 BTU/h, half a ton or 1.76 kW. Energy Star's sizing chart, based on 8 ft ceilings, lists 8,000 BTU/h for 300 up to 350 ft², so its figure is shown alongside for rooms of 100 to 2,500 ft².

Both are estimates for one room. For a whole house, ACCA describes its Manual J as the ANSI-recognised method for equipment sizing loads.

## Входные данные

- **Площадь комнаты**
- **Ceiling height**
- **Insulation** (варианты: Good, Среднее, Poor)
- **Sun exposure** (варианты: Heavily shaded, Normal, Very sunny)
- **People who regularly use the room**
- **The room is a kitchen**

## Результаты

- Cooling load (BTU/h) — основной результат
- Cooling load (tons)
- Cooling load (kW)
- Next common unit size (BTU/h)
- Energy Star chart for this area (BTU/h)

## Формула

$$
Q = 20\,A\,\frac{h}{8}\,f_{\text{ins}}\,f_{\text{sun}} + 600\max(0, p - 2) + 4000\,[\text{kitchen}]
$$

## Примеры с решением

### 300 ft² room, 8 ft ceiling, average everything

- Площадь комнаты: 300 ft²
- Ceiling height: 8 ft
- Insulation: Среднее
- Sun exposure: Normal
- People who regularly use the room: 2
- **Cooling load: 6,000 BTU/h**
- **Cooling load: 0.5 tons**
- **Cooling load: 1.76 kW**
- **Next common unit size: 6,000 BTU/h**
- **Energy Star chart for this area: 8,000 BTU/h**
- Источник проверки: Python decimal: 300 × 20 = 6,000 BTU/h ÷ 12,000 = 0.5 ton × 0.29307 = 1.758 kW; Energy Star chart row 300–350 ft² = 8,000

### Sunny 400 ft² kitchen, 10 ft ceiling, poor insulation, 4 people

- Площадь комнаты: 400 ft²
- Ceiling height: 10 ft
- Insulation: Poor
- Sun exposure: Very sunny
- People who regularly use the room: 4
- The room is a kitchen: да
- **Cooling load: 18,400 BTU/h**
- **Cooling load: 1.53 tons**
- **Next common unit size: 24,000 BTU/h**
- **Energy Star chart for this area: 16,200 BTU/h**
- Источник проверки: Python decimal: 400 × 20 × 1.25 × 1.2 × 1.1 + 2 × 600 + 4,000 = 18,400; Energy Star 10,000 × 1.1 + 1,200 + 4,000 = 16,200

### Shaded 20 m² bedroom, 2.4 m ceiling, good insulation, 1 person

- Площадь комнаты: 20 m²
- Ceiling height: 2.4 m
- Insulation: Good
- Sun exposure: Heavily shaded
- People who regularly use the room: 1
- **Cooling load: 3,433 BTU/h**
- **Next common unit size: 5,000 BTU/h**
- **Energy Star chart for this area: 5,400 BTU/h**
- Источник проверки: Python decimal: 215.28 ft² × 20 × (7.874/8) × 0.9 × 0.9 = 3,432.6 BTU/h; one occupant adds nothing; chart 6,000 × 0.9

### Edge: 150 ft² sits on a chart boundary

- Площадь комнаты: 150 ft²
- Ceiling height: 8 ft
- Insulation: Среднее
- Sun exposure: Normal
- People who regularly use the room: 2
- **Cooling load: 3,000 BTU/h**
- **Energy Star chart for this area: 6,000 BTU/h**
- Источник проверки: Energy Star chart: 150 ft² falls in the “150 up to 250” row (6,000 BTU/h); rule of thumb 150 × 20 = 3,000

## Вопросы

### What size air conditioner do I need for my room?

Energy Star's chart for 8 ft ceilings lists 5,000 BTU/h for 100–150 ft², 6,000 for 150–250 ft², 8,000 for 300–350 ft², 10,000 for 400–450 ft², 12,000 for 450–550 ft² and 18,000 for 700–1,000 ft². The 20 BTU/h per ft² rule gives less for small rooms, 6,000 against 8,000 at 300 ft², so the chart figure is shown beside the result.

### How many BTU per square foot do I need?

This calculator uses 20 BTU/h per square foot for an 8 ft ceiling. Energy Star's chart works out higher for small and mid-sized rooms: 8,000 BTU/h for 300 ft² is about 27 per ft², and 12,000 BTU/h for 450 ft² is also about 27. At 1,000 ft² the chart's 21,000 BTU/h is 21 per ft², close to the rule.

### How many BTU is a ton of air conditioning?

One ton of refrigeration is 12,000 BTU/h, which NIST SP 811 lists as 3,516.853 W; one BTU/h is 0.2930711 W. A 6,000 BTU/h room unit is therefore half a ton or 1.76 kW of cooling, and a 24,000 BTU/h split system is 2 tons or 7.03 kW.

### Is a bigger air conditioner better?

No. Energy Star says an oversized unit costs more to buy, wastes energy and does not cool better: it cools the room before it has time to remove the humidity, leaving the air damp and clammy. Choose the unit size that matches the load rather than rounding up by a full size or more for safety.

### How do ceiling height and sunlight change the BTU needed?

Energy Star's chart assumes 8 ft ceilings, and this calculator scales the load in proportion to height, so a 10 ft ceiling adds 25%. Energy Star advises 10% less capacity for a heavily shaded room and 10% more for a very sunny one, plus 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h in a kitchen.

### Насколько точен «Air conditioner BTU calculator»?

Точность зависит от введённых данных и допущений метода. Десятичная арифметика использует 50 значащих цифр, но оценки, численные методы и исходные данные могут быть менее точными; округление на экране не устраняет эти ограничения. Решённые примеры, проверенные по независимым источникам: 4. Например, «300 ft² room, 8 ft ceiling, average everything» проверяется по источнику Python decimal: 300 × 20 = 6,000 BTU/h ÷ 12,000 = 0.5 ton × 0.29307 = 1.758 kW; Energy Star chart row 300–350 ft² = 8,000.

### Откуда взята методика?

ENERGY STAR — Room air conditioners: sizing chart and adjustments; ACCA Manual J 8th Edition (ANSI/ACCA 2 Manual J – 2016) — residential load calculation; NIST SP 811 Appendix B.9 — ton of refrigeration and BTU/h to watt.

## Источники

- [ENERGY STAR — Room air conditioners: sizing chart and adjustments](https://www.energystar.gov/products/room_air_conditioners)
- [ACCA Manual J 8th Edition (ANSI/ACCA 2 Manual J – 2016) — residential load calculation](https://www.acca.org/standards/technical-manuals/manual-j)
- [NIST SP 811 Appendix B.9 — ton of refrigeration and BTU/h to watt](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9)