BTU for HVAC
Sizing Your Heating and Cooling Equipment
Calculate Your NeedsShopping for an air conditioner or furnace means confronting BTU ratings—5,000 BTU, 12,000 BTU, 80,000 BTU. What do these numbers mean, and how do you know what size you need? 理解する BTUs helps you choose equipment that's neither too small (won't cool/heat effectively) nor too large (wastes energy and money).
BTU in HVAC Context
For Cooling (Air Conditioners)
BTU/hr indicates how much heat the unit can remove from your space per hour. A 12,000 BTU/hr AC removes 12,000 BTUs of heat from your room every hour.
This equals 1 "ton" of cooling—a term from the ice age when cooling capacity was measured by how much ice would melt.
For Heating (Furnaces, Heaters)
BTU/hr indicates how much heat the unit produces per hour. An 80,000 BTU furnace produces 80,000 BTUs of heat hourly when running at full capacity.
Room Size Guidelines
Air Conditioning
| Room Size (sq ft) | BTU Needed | Example Room |
|---|---|---|
| 100-150 | 5,000 | Small bedroom |
| 150-250 | 6,000 | Average bedroom |
| 250-350 | 8,000 | Large bedroom |
| 350-450 | 10,000 | Small living room |
| 450-550 | 12,000 (1 ton) | Average living room |
| 550-700 | 14,000 | Large living room |
| 700-1,000 | 18,000 | Great room |
| 1,000-1,200 | 24,000 (2 tons) | Large open space |
These are baseline estimates. Adjust for factors below.
Adjustment Factors
Modify your BTU needs based on:
| Factor | Adjustment |
|---|---|
| Sunny room | +10% |
| Shaded room | -10% |
| Kitchen | +4,000 BTU |
| More than 2 occupants | +600 BTU per person |
| High ceilings (10+ ft) | +10-25% |
| Poor insulation | +10-30% |
| Hot climate (AZ, TX, FL) | +10-20% |
| Very cold climate (MN, WI) | +10-20% (heating) |
Whole-House HVAC Sizing
Central Air Conditioning
| Home Size (sq ft) | Cooling Capacity | 変換先ns |
|---|---|---|
| 600-1,000 | 18,000-24,000 BTU | 1.5-2 |
| 1,000-1,500 | 24,000-36,000 BTU | 2-3 |
| 1,500-2,000 | 36,000-48,000 BTU | 3-4 |
| 2,000-2,500 | 48,000-60,000 BTU | 4-5 |
| 2,500-3,000 | 60,000-72,000 BTU | 5-6 |
Furnaces
| Home Size (sq ft) | Cold Climate | Moderate Climate | Warm Climate |
|---|---|---|---|
| 1,000 | 45,000 BTU | 35,000 BTU | 25,000 BTU |
| 1,500 | 67,500 BTU | 52,500 BTU | 37,500 BTU |
| 2,000 | 90,000 BTU | 70,000 BTU | 50,000 BTU |
| 2,500 | 112,500 BTU | 87,500 BTU | 62,500 BTU |
BTU Conversions
| Unit | BTU Equivalent |
|---|---|
| 1 kWh | 3,412 BTU |
| 1 therm (gas) | 100,000 BTU |
| 1 ton (cooling) | 12,000 BTU/hr |
| 1 gallon propane | 91,500 BTU |
| 1 gallon heating oil | 138,500 BTU |
| 1 cubic foot natural gas | 1,030 BTU |
Efficiency Ratings
Air Conditioners: SEER
Seasonal Energy Efficiency Ratio—higher is better. Minimum standard is 14 SEER; high-efficiency units reach 20+ SEER.
Furnaces: AFUE
Annual Fuel Utilization Efficiency—percentage of fuel converted to heat. Standard is 80% AFUE; high-efficiency condensing furnaces reach 95-98% AFUE.
Heat Pumps: HSPF
Heating Seasonal Performance Factor—higher is better. Minimum is 8.2 HSPF; efficient units reach 10+.
まとめ
BTU ratings tell you the heating or cooling capacity of HVAC equipment. For room ACs, use roughly 20 BTU per square foot as a starting point, then adjust for room conditions. For whole-house systems, work with a contractor who can perform proper load calculations. Properly sized equipment runs more efficiently, provides better comfort, and lasts longer than oversized or undersized units.