BTU Calculator
Common AC Unit Sizes
Quick BTU Guide
Related Calculators
Understanding BTU
What is a BTU?
BTU stands for British Thermal Unit, which measures thermal energy. One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is commonly used to rate the capacity of heating and cooling systems.
Basic Calculation
Factors Affecting BTU Requirements
| Factor | Impact | Adjustment |
|---|---|---|
| Heavy Sun Exposure | Increases cooling load | +10% |
| Heavy Shade | Reduces cooling load | -10% |
| Kitchen Use | Heat from appliances | +4,000 BTU |
| High Ceilings (10ft+) | More volume to condition | +20% |
| Each Additional Person | Body heat | +600 BTU |
Heating vs Cooling
Heating (Furnace/Heat Pump)
- 30-60 BTU per sq ft
- Climate zone matters most
- Insulation quality critical
- Consider AFUE efficiency rating
- Size for coldest expected days
Cooling (Air Conditioner)
- 20-30 BTU per sq ft
- Sun exposure important
- Humidity affects comfort
- Check SEER efficiency rating
- Oversizing wastes energy
AC Unit Sizing Chart
1 Ton of cooling = 12,000 BTU/hour
Sizing Tips
An oversized unit will cycle on and off frequently, reducing efficiency and humidity control. An undersized unit will run constantly and struggle to maintain temperature. For best results, have a professional perform a Manual J load calculation.
Frequently Asked Questions
What is a BTU?
BTU stands for British Thermal Unit, a measure of thermal energy. One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. HVAC systems are rated by their BTU capacity per hour.
How many BTUs do I need per square foot?
For cooling, you typically need 20-30 BTU per square foot. For heating, you need 30-60 BTU per square foot depending on your climate zone. Factors like ceiling height, insulation quality, sun exposure, and number of windows affect these requirements.
What size air conditioner do I need for my room?
A rough guide: 150-250 sq ft needs 5,000 BTU, 250-350 sq ft needs 8,000 BTU, 350-450 sq ft needs 10,000 BTU, and 450-700 sq ft needs 14,000 BTU. Adjust up for sunny rooms, kitchens, or high ceilings; adjust down for shaded areas.
What happens if my AC is oversized?
An oversized air conditioner will cycle on and off too frequently, reducing efficiency and humidity control. It won't properly dehumidify the air, leading to a cold but clammy feeling. It also wastes energy and shortens equipment life.