14 Inch Duct Calculator
What is the CFM for a 14 inch duct? Calculate airflow capacity, velocity limits, and rectangular equivalents for 14" HVAC ducts. Includes metal and flex duct notes.
Airflow Capacity for 14" Round Duct
A 14 inch round duct has a cross sectional area of 153.9 square inches (1.069 sq ft). The table below shows the CFM airflow at different air velocities.
| Velocity (FPM) | Airflow (CFM) | Noise Level | Use Case |
|---|---|---|---|
| 600 FPM | 641 CFM | ✅ Quiet | Residential supply |
| 700 FPM | 748 CFM | ✅ Quiet | Residential supply |
| 800 FPM | 855 CFM | ⚠️ Moderate | Commercial supply |
| 900 FPM | 962 CFM | 🔊 May be noisy | Industrial |
Technical Specifications
Rectangular Equivalent
20x8 or 18x10 inches
Based on ASHRAE equivalent diameter formulas.
Max Recommended CFM
962 CFM
Based on 900 FPM (max residential velocity).
14 Inch Metal vs. Flex Duct
While the nominal diameter is the same, 14" flexible duct has significantly higher air resistance than smooth 14" galvanized sheet metal duct.
- Metal Duct: Delivers approximately 748 CFM at 0.1 friction rate.
- Flex Duct: Usually requires a 1.5x resistance factor. To deliver the same airflow, you may need to increase to a 16" flex duct.
- Return Air: For a return duct, a 14" round duct is generally limited to 535 CFM to maintain quiet operation (600 FPM).
Frequently Asked Questions
How much CFM can a 14 inch duct handle?
A 14 inch round duct can handle between 535 and 962 CFM. For residential supply branches, it is typically used for 748 CFM at 0.08 friction rate.
What is the rectangular equivalent of 14" round?
The most common rectangular equivalents for a 14 inch round duct are 20x8 or 18x10 inches.
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