1. What is an HVAC Vent Size Calculator?

Definition: This calculator determines the required duct area based on airflow (CFM) and desired air velocity.

Purpose: It helps HVAC professionals and engineers properly size ductwork for efficient air distribution.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( A \) — Duct cross-sectional area (square inches)
• \( Q \) — Airflow rate (cubic feet per minute, CFM)
• \( V \) — Air velocity (feet per minute, FPM)
• 144 — Conversion factor (sq ft to sq in)

Explanation: The CFM is divided by velocity to get area in square feet, then converted to square inches.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing ensures efficient airflow, proper system performance, noise reduction, and energy efficiency.

4. Using the Calculator

Tips: Enter the CFM (airflow rate) and desired velocity (default 800 FPM for supply ducts). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical velocity for HVAC ducts?
A: Supply ducts: 600-900 FPM, Return ducts: 500-700 FPM, depending on application and noise requirements.

Q2: Why convert to square inches?
A: Duct sizes are commonly specified in inches (e.g., 8x12 duct) rather than square feet.

Q3: How do I determine CFM for a room?
A: Calculate based on room volume and required air changes per hour, or use heat load calculations.

Q4: What about round ducts?
A: Convert the square inch result to diameter using \( D = 2 \times \sqrt{A/\pi} \).

Q5: Does this account for pressure drop?
A: No, this is a basic calculation. For detailed design, consider friction rate and static pressure.