1. What is Duct Sizing?

Duct sizing is the process of determining the appropriate dimensions for HVAC ductwork to efficiently distribute air throughout a building. Proper duct sizing ensures optimal system performance, energy efficiency, and occupant comfort.

2. How Does the Calculator Work?

The calculator uses the basic duct sizing formula:

Where:

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

Explanation: The formula calculates the required duct 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 system efficiency, proper air distribution, noise control, and energy savings. Undersized ducts can cause high velocity noise and reduced airflow, while oversized ducts can lead to poor air distribution and increased installation costs.

4. Using the Calculator

Tips:

• For supply ducts, typical velocities range from 600-900 fpm for main ducts and 500-700 fpm for branch ducts
• For return ducts, use 500-700 fpm for main ducts and 300-500 fpm for branch ducts
• Higher velocities may be used in commercial applications, while lower velocities are preferred in residential for noise control

5. Frequently Asked Questions (FAQ)

Q1: What is the recommended air velocity for residential HVAC systems?
A: For residential systems, recommended velocities are typically 600-900 fpm for supply ducts and 500-700 fpm for return ducts to balance efficiency and noise.

Q2: How do I convert duct area to round duct diameter?
A: For round ducts, diameter can be calculated using \( D = 2 \times \sqrt{A/\pi} \), where A is the cross-sectional area.

Q3: What factors affect duct sizing besides CFM and velocity?
A: Duct material, system static pressure, duct length, number of bends, and thermal insulation all affect final duct sizing decisions.

Q4: Should I use the same velocity for all ducts in a system?
A: No, main ducts typically use higher velocities than branch ducts to maintain proper air distribution while controlling noise in occupied spaces.

Q5: How does duct sizing affect energy efficiency?
A: Properly sized ducts reduce energy consumption by minimizing pressure drop and allowing the system to operate at peak efficiency.