Understanding Your AC's BTU Requirement
**BTU (British Thermal Unit)** is the standard measure of an air conditioner's cooling capacity. It defines the amount of heat an AC unit can remove from a room in one hour. Sizing an AC unit correctly to its required **BTUs per hour** is the most critical step for achieving comfort and energy efficiency.
Standard BTU to Area Chart
Use this chart as a general starting point for a room with an 8-foot ceiling and average sun exposure. This table does not include load adjustments.
| Room Area (Square Feet) | BTUs Needed (Approx.) | Equivalent Tonnage |
|---|---|---|
| 100 - 150 sq ft | 5,000 - 6,000 BTUs | 0.4 - 0.5 Ton |
| 150 - 250 sq ft | 7,000 - 8,000 BTUs | 0.6 - 0.7 Ton |
| 250 - 400 sq ft | 9,000 - 10,000 BTUs | 0.75 - 0.8 Ton |
| 400 - 550 sq ft | 12,000 BTUs | 1.0 Ton |
| 550 - 700 sq ft | 14,000 BTUs | 1.2 Ton |
| 700 - 1,000 sq ft | 18,000 BTUs | 1.5 Ton |
| 1,000+ sq ft | 24,000+ BTUs | 2.0+ Tons |
Why Proper BTU Sizing is Critical
If the AC Unit is **Oversized** (Too Many BTUs):
- **Poor Dehumidification:** The room cools too quickly, causing the unit to shut off before it runs long enough to pull sufficient moisture out of the air. This leaves the room feeling clammy and cold.
- **Higher Energy Bills:** The unit constantly cycles on and off ("short cycling"), which consumes a lot of power and causes faster wear and tear on the components.
- **Temperature Swings:** You get brief blasts of very cold air, followed by a quick warm-up.
If the AC Unit is **Undersized** (Too Few BTUs):
- **Continuous Running:** The unit runs non-stop, especially on hot days, without ever reaching the set temperature.
- **High Energy Bills:** Running constantly, the unit consumes maximum energy for minimal comfort gain.
- **Component Failure:** The continuous operation puts enormous strain on the compressor, significantly shortening the unit's lifespan.
Quick Conversion Fact
The term **Tonnage** is an old measure: 1 ton of AC capacity is the amount of cooling produced by one ton of melting ice over 24 hours. That is mathematically equal to $\mathbf{12,000}$ **BTUs/hr.**