1. What is the Duct Size Calculation?

The duct size calculation determines the cross-sectional area needed for air ducts in HVAC systems based on airflow (CFM) and velocity. Proper duct sizing is essential for efficient air distribution and system performance.

2. How Does the Calculator Work?

The calculator uses the duct sizing formula:

Where:

• \( A \) — Duct cross-sectional area (sq ft)
• \( CFM \) — Airflow in cubic feet per minute
• \( V \) — Air velocity in feet per minute

Explanation: The formula calculates the required duct area to maintain a specific air velocity for a given airflow rate.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient airflow, reduces energy consumption, minimizes noise, and maintains proper air pressure throughout the HVAC system.

4. Using the Calculator

Tips: Enter CFM (airflow rate) and desired air velocity. Both values must be positive numbers. Typical velocities range from 600-900 ft/min for supply ducts and 500-700 ft/min for return ducts.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical CFM range for residential HVAC?
A: Residential systems typically range from 800-2000 CFM, depending on the size of the home and system capacity.

Q2: What velocity is recommended for different duct types?
A: Supply ducts: 600-900 ft/min, Return ducts: 500-700 ft/min, Low-velocity systems: 400-600 ft/min.

Q3: How does duct shape affect sizing?
A: Round ducts are more efficient than rectangular ducts. When using rectangular ducts, maintain equivalent cross-sectional area for proper airflow.

Q4: What factors affect duct sizing besides CFM and velocity?
A: Duct material, length, number of bends, static pressure, and temperature differences all affect final duct sizing requirements.

Q5: Should I always use the minimum duct size calculated?
A: It's often better to slightly oversize ducts to reduce air resistance and noise, but balance this with space constraints and cost considerations.