Duct Size Calculator
Calculate optimal duct sizes for HVAC systems based on airflow requirements.
Airflow Parameters
Duct Configuration
Duct Dimensions
Recommended round duct diameter
Performance Metrics
Actual air velocity based on calculated size
Total pressure loss including friction
Recommendations
Velocity
Velocity is within recommended range
Size
Size dimensions are appropriate
Installation
Ensure proper sealing and insulation
Maintenance
Schedule regular inspections and cleaning
Understanding Duct Sizing
Proper duct sizing is crucial for HVAC system efficiency and performance. This calculator helps you determine the optimal duct size based on your airflow requirements and desired air velocity. Whether you're working with round or rectangular ducts, accurate sizing ensures proper air distribution while minimizing noise and energy loss.
Key Concepts
Airflow (CFM)
Cubic Feet per Minute (CFM) measures the volume of air flowing through the duct. Higher CFM values indicate greater air movement and typically require larger duct sizes.
Air Velocity (FPM)
Feet per Minute (FPM) measures how fast air moves through the duct. Balancing velocity is crucial - too slow allows debris settling, too fast creates noise and wastes energy.
Using the Calculator
- Enter your required airflow in CFM
- Input the desired air velocity in FPM
- Select between round or rectangular duct shape
- For rectangular ducts, specify the maximum aspect ratio if needed
- Review the calculated dimensions and recommendations
Important Considerations
- Velocity Ranges: Residential ducts typically use 600-1000 FPM, commercial 1000-1500 FPM, and industrial 1500-2500 FPM
- Aspect Ratio: For rectangular ducts, maintain a width-to-height ratio below 4:1 for optimal performance
- Pressure Loss: Consider pressure drops when designing longer duct runs or systems with multiple fittings
- Installation: Ensure proper sealing and insulation to maintain system efficiency
Best Practices
Design
- • Minimize the use of flexible ducts
- • Use gradual transitions and turns
- • Account for future system expansion
- • Consider noise requirements
Installation
- • Properly support ductwork
- • Seal all joints and seams
- • Insulate when necessary
- • Follow local codes
Maintenance
- • Regular inspections
- • Clean ducts periodically
- • Check for air leaks
- • Monitor system performance