🔥 Furnace Size Calculator
Calculate the right furnace size (BTU) for your home
Total heated area of your home
Approximate number of large windows (for heat loss calculation)
How to Use This Calculator
Enter Home Square Footage
Input the total heated square footage of your home. This is the area that needs heating, excluding unheated spaces like garages.
Enter Ceiling Height
Input the average ceiling height in feet (standard is 9 feet). Higher ceilings require more heating capacity.
Select Climate and Insulation
Choose your climate zone (cold, moderate, warm) and insulation quality (poor, average, good). These factors significantly affect heating requirements.
Calculate and Review
Click "Calculate Furnace Size" to see recommended BTU, closest standard size, and estimated cost. Consult an HVAC professional for accurate sizing.
Formula
BTU per sq ft = Base BTU (varies by climate and insulation)
Base BTU = Square Footage × BTU per sq ft
Adjusted BTU = Base BTU × (Ceiling Height ÷ 9) × Window Factor
Recommended BTU = Round up to nearest 10,000 BTU
Tons = BTU ÷ 12,000 (1 ton = 12,000 BTU)
Example 1: Moderate Climate, Average Insulation (2000 sq ft, 9 ft ceilings)
Step 1: BTU per sq ft: 35 BTU/sq ft (moderate climate, average insulation)
Step 2: Base BTU: 2000 × 35 = 70,000 BTU
Step 3: Adjusted for ceiling: 70,000 × (9/9) = 70,000 BTU
Step 4: Round up: 80,000 BTU (recommended size)
Step 5: Convert to tons: 80,000 ÷ 12,000 = 6.7 tons
Example 2: Cold Climate, Poor Insulation (2500 sq ft, 10 ft ceilings, 12 windows)
Step 1: BTU per sq ft: 50 BTU/sq ft (cold climate, poor insulation)
Step 2: Base BTU: 2500 × 50 = 125,000 BTU
Step 3: Adjusted for ceiling: 125,000 × (10/9) = 138,889 BTU
Step 4: Adjusted for windows: 138,889 × 1.6 = 222,222 BTU
Step 5: Round up: 180,000 BTU (closest standard size)
About Furnace Size Calculator
The Furnace Size Calculator is an essential tool for homeowners, contractors, and HVAC professionals who need to determine the right furnace size (BTU) for home heating. This calculator eliminates guesswork by providing precise furnace sizing calculations based on square footage, ceiling height, climate zone, insulation quality, and windows, helping you select the right furnace size for efficient and effective heating.
When to Use This Calculator
- New Furnace Installation: Calculate furnace size needed for new furnace installations
- Furnace Replacement: Determine correct furnace size when replacing existing furnace
- Home Addition: Calculate additional heating capacity needed for home additions
- Budget Planning: Estimate furnace costs based on required size
- HVAC Planning: Plan HVAC systems for new construction or renovations
Why Use Our Calculator?
- ✅ Accurate Sizing: Precise calculations prevent undersizing or oversizing
- ✅ Multiple Factors: Considers climate, insulation, ceiling height, and windows
- ✅ Standard Sizes: Recommends closest standard furnace size
- ✅ Cost Estimation: Provides estimated costs based on furnace size
- ✅ Comprehensive Results: Shows BTU, tons, and cubic footage
- ✅ Time Savings: Instant calculations eliminate manual math and measurements
Common Applications
New Furnace Installation: Homeowners and contractors installing new furnaces use this calculator to determine correct furnace size. Proper sizing ensures efficient heating and energy savings while preventing undersizing or oversizing.
Furnace Replacement: Homeowners replacing existing furnaces use this tool to verify or recalculate furnace size. Home improvements like better insulation may allow for smaller furnaces, while additions may require larger furnaces.
Budget Planning: Homeowners and contractors use this calculator to estimate furnace costs based on required size, helping plan budgets and compare options.
Tips for Best Results
- Measure Accurately: Measure heated square footage accurately (exclude unheated spaces)
- Consider All Factors: Account for climate, insulation, ceiling height, and windows
- Consult Professional: Always consult an HVAC professional for accurate sizing and installation
- Energy Efficiency: Consider energy-efficient furnaces for lower operating costs
- Ductwork: Ensure ductwork can handle furnace size
- Local Codes: Check local building codes for furnace requirements
Frequently Asked Questions
What size furnace do I need for a 2000 sq ft home?
For a 2000 sq ft home in a moderate climate with average insulation, you typically need 60,000-80,000 BTU furnace. Actual size depends on climate, insulation, ceiling height, and windows. Use the calculator with your specific details for accurate sizing.
How many BTUs per square foot do I need?
BTU per square foot varies by climate and insulation: 20-30 BTU/sq ft for warm climates, 30-40 BTU/sq ft for moderate climates, and 40-50 BTU/sq ft for cold climates. Better insulation reduces BTU requirements. The calculator adjusts for these factors.
Can a furnace be too big?
Yes! An oversized furnace cycles frequently, reducing efficiency, increasing wear, and creating temperature swings. Undersizing causes inadequate heating. Proper sizing is essential for efficiency and comfort. Always consult an HVAC professional.
What are standard furnace sizes?
Standard furnace sizes are typically 40,000, 60,000, 80,000, 100,000, 120,000, 140,000, 160,000, 180,000, and 200,000 BTU. The calculator recommends the closest standard size to your requirements.
How do I convert BTU to tons?
Divide BTU by 12,000 to get tons (1 ton = 12,000 BTU). For example, 80,000 BTU ÷ 12,000 = 6.7 tons. The calculator automatically converts BTU to tons for easy reference.
Should I consult a professional?
Yes! While this calculator provides estimates, furnace sizing is complex and requires professional assessment. An HVAC professional considers many additional factors like ductwork, windows, doors, construction type, and local codes for accurate sizing and installation.