Air Conditioner Duct Size Calculator

Duct Area Formula:

\[ \text{Duct Area} = \frac{\text{CFM}}{\text{Velocity}} \]

CFM (Cubic Feet per Minute):

ft³/min

Velocity:

fpm

Output Unit:

Duct Area:

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1. What is Duct Area Calculation?

Duct area calculation determines the cross-sectional area required for airflow in HVAC systems. Proper duct sizing ensures efficient air distribution, adequate airflow, and optimal system performance while minimizing energy consumption and noise.

2. How Does the Calculator Work?

The calculator uses the fundamental duct sizing formula:

\[ \text{Duct Area} = \frac{\text{CFM}}{\text{Velocity}} \]

Where:

\( \text{CFM} \) — Airflow rate in cubic feet per minute
\( \text{Velocity} \) — Air velocity in feet per minute (fpm)
\( \text{Duct Area} \) — Cross-sectional area in square feet or inches

Explanation: This formula calculates the required duct cross-sectional area based on the desired airflow rate and air velocity. Higher velocities require smaller ducts but increase noise and pressure drop.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing is crucial for HVAC system efficiency. Undersized ducts cause high static pressure, reduced airflow, and increased energy consumption. Oversized ducts lead to poor air distribution and velocity issues.

4. Using the Calculator

Tips: Enter CFM (cubic feet per minute), select appropriate velocity (typically 600-900 fpm for supply, 500-700 fpm for return), and choose output unit (square feet or square inches). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the recommended velocity for residential ducts?
A: Supply ducts: 600-900 fpm, Return ducts: 500-700 fpm. Lower velocities reduce noise but require larger ducts.

Q2: How does duct shape affect the calculation?
A: This calculator provides area. For rectangular ducts, use Area = Width × Height. For round ducts, use Area = π × (Diameter/2)².

Q3: What factors influence duct sizing?
A: Airflow requirements, system static pressure, duct material, layout complexity, and noise considerations all affect optimal duct sizing.

Q4: When should I use higher velocities?
A: Higher velocities (up to 1200 fpm) may be used in commercial applications or where space constraints require smaller ducts, but noise levels increase.

Q5: How accurate is this calculation for real-world applications?
A: This provides basic sizing. Professional HVAC design should consider friction losses, fittings, and system-specific requirements for optimal performance.