AC Duct Size Calculator

Duct Area Formula:

\[ \text{Area (ft²)} = \frac{\text{CFM}}{\text{Velocity (FPM)}} \]

Duct Area:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is AC Duct Size Calculation?

AC duct size calculation determines the cross-sectional area required for proper airflow in HVAC systems. Proper duct sizing ensures efficient air distribution, optimal system performance, and energy efficiency.

2. How Does the Calculator Work?

The calculator uses the duct area formula:

\[ \text{Area (ft²)} = \frac{\text{CFM}}{\text{Velocity (FPM)}} \]

Where:

\( \text{CFM} \) — Cubic Feet per Minute (airflow rate)
\( \text{Velocity} \) — Feet per Minute (air velocity)
\( \text{Area} \) — Square Feet (duct cross-sectional area)

Explanation: This formula calculates the required duct area based on the desired airflow rate and velocity to ensure proper air distribution throughout the HVAC system.

3. Importance of Proper Duct Sizing

Details: Correct duct sizing is crucial for maintaining proper air pressure, minimizing energy consumption, reducing noise levels, and ensuring even temperature distribution throughout the building.

4. Using the Calculator

Tips: Enter CFM (airflow rate) and velocity in FPM. Typical residential duct velocities range from 600-900 FPM for supply ducts and 500-700 FPM for return ducts. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the recommended velocity for residential ducts?
A: For supply ducts: 600-900 FPM, for return ducts: 500-700 FPM. Lower velocities reduce noise but require larger ducts.

Q2: How does duct size affect system performance?
A: Undersized ducts cause high velocity, noise, and pressure drops. Oversized ducts reduce velocity, potentially causing poor air distribution and temperature stratification.

Q3: What factors influence CFM requirements?
A: Room size, insulation quality, window area, climate zone, and the specific heating/cooling load calculations for each space.

Q4: Can I use this for round ducts?
A: Yes, the area calculation applies to both rectangular and round ducts. For round ducts, use the formula: Diameter = 2 × √(Area/π).

Q5: What are common duct materials and their impact?
A: Sheet metal (smooth, efficient), flex duct (easy installation but higher friction), and fiberglass duct board (good insulation but rough surface increases friction).