1. What is the Duct Size Calculation?

The duct size calculation determines the appropriate dimensions for HVAC return ducts based on airflow (CFM) and velocity. Proper duct sizing is essential for efficient HVAC system operation and optimal airflow.

2. How Does the Calculator Work?

The calculator uses the duct size formula:

Where:

• \( CFM \) — Cubic feet per minute (airflow rate)
• \( Velocity \) — Air velocity in feet per minute
• \( 144 \) — Conversion factor (12² for square inches)

Explanation: The formula calculates the duct cross-sectional area needed to maintain proper airflow at the specified velocity.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient HVAC operation, proper airflow, reduced energy consumption, and prevents issues like noise, pressure imbalances, and system strain.

4. Using the Calculator

Tips: Enter CFM (cubic feet per minute) and velocity (feet per minute). Both values must be positive numbers. Typical residential velocities range from 600-900 ft/min for return ducts.

5. Frequently Asked Questions (FAQ)

Q1: What is CFM in HVAC systems?
A: CFM (cubic feet per minute) measures airflow volume. It indicates how much air moves through the ductwork in one minute.

Q2: What velocity should I use for return ducts?
A: For residential systems, 600-900 ft/min is typical for return ducts. Lower velocities reduce noise but require larger ducts.

Q3: Why is the result in inches?
A: The calculation provides the duct diameter for round ducts or the side length for square ducts in inches, which is standard for HVAC measurements.

Q4: Does this work for both round and rectangular ducts?
A: This calculation provides the equivalent diameter for round ducts. For rectangular ducts, additional calculations are needed to maintain the same cross-sectional area.

Q5: What happens if ducts are undersized?
A: Undersized ducts cause restricted airflow, reduced efficiency, increased noise, higher energy costs, and potential system damage from overworking.