1. What is the Duct Size CFM Formula?

The duct size formula calculates the required cross-sectional area of a duct based on airflow rate (CFM) and air velocity. Proper duct sizing is essential for efficient HVAC system operation and optimal airflow distribution.

2. How Does the Calculator Work?

The calculator uses the duct size formula:

Where:

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

Explanation: The formula calculates the required duct area by dividing the airflow rate by the desired air velocity.

3. Importance of Proper Duct Sizing

Details: Proper duct sizing is crucial for maintaining efficient HVAC system operation, ensuring adequate airflow, minimizing energy consumption, and reducing noise levels in ventilation systems.

4. Using the Calculator

Tips: Enter CFM (cubic feet per minute) and desired air velocity (feet per minute). All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical air velocity for HVAC ducts?
A: Residential systems typically use 600-900 ft/min for supply ducts and 500-700 ft/min for return ducts.

Q2: How does duct shape affect the calculation?
A: This formula calculates area. For rectangular ducts, you'll need to determine appropriate width and height dimensions that provide the calculated area.

Q3: What happens if ducts are undersized?
A: Undersized ducts can cause reduced airflow, increased noise, higher energy consumption, and strain on HVAC equipment.

Q4: Are there industry standards for duct sizing?
A: Yes, organizations like ACCA (Air Conditioning Contractors of America) provide standards such as Manual D for residential duct design.

Q5: Should I consider static pressure in duct design?
A: Yes, static pressure calculations are also important for complete duct system design and proper fan selection.