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A browser-based hvac duct air velocity calculator tool. No data sent to server.

📘 How to Use

  1. Enter the airflow rate in CFM.
  2. Select the duct shape (Circular or Rectangular).
  3. Input the duct dimensions in inches (diameter, or width and height).
  4. Instantly view the calculated velocity, dynamic pressure, and recommended application.

HVAC Duct Air Velocity Calculator

Duct Velocity
0.00 ft/min
Dynamic Pressure (Std. Air)
0.00 in.wg
Recommended Use (Noise ref)
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Article

HVAC Duct Velocity Calculator | Airflow & Sizing Tool

This online calculator determines the air velocity and dynamic pressure within HVAC ductwork based on airflow rate and duct dimensions. It is an essential tool for HVAC engineers, technicians, and system designers to quickly verify designs, size ducts, and troubleshoot airflow issues according to industry standards.

💡 Tool Overview

  • Comprehensive Calculations: Instantly computes air velocity in feet per minute (ft/min) and dynamic pressure in inches of water gauge (in.wg).
  • Flexible Duct Shapes: Supports calculations for both standard circular and rectangular duct profiles.
  • Application Diagnosis: Provides a practical, color-coded recommendation for the calculated velocity's suitability (e.g., Residential, Office, Industrial), based on ASHRAE noise and performance guidelines.
  • Imperial Units: Designed for the US market and engineering standards, accepting inputs in CFM (Cubic Feet per Minute) and inches.

🧐 Frequently Asked Questions

Q. What standard is the "Recommended Use" diagnosis based on?

A. The recommendations are based on widely accepted air velocity ranges from industry standards, such as those published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). These guidelines help ensure that duct designs meet acoustic (noise level) and energy efficiency (friction loss) requirements for their intended application.

Q. What is dynamic pressure (in.wg)?

A. Dynamic pressure is the kinetic pressure exerted by air in motion. It is a direct function of air velocity and density. In HVAC design, it is a key component of the total pressure a fan must overcome to move air through the system. This calculator computes it for standard air density.

📚 Duct Sizing Principles

Proper duct sizing is a critical aspect of HVAC system design, involving a trade-off between performance, cost, and space. The air velocity within a duct is a primary factor in this balance.

  • High Velocity: Using smaller ducts results in higher air velocity. While this saves material costs and space, it also leads to increased friction loss, which requires more fan power and consumes more energy. Furthermore, high velocities are a primary source of undesirable noise (breakout noise and terminal noise at diffusers).

  • Low Velocity: Using larger ducts results in lower velocity. This minimizes noise and reduces friction loss, leading to lower energy consumption. However, it significantly increases the initial material and installation costs and requires more physical space in ceilings and walls. This tool helps you quickly assess if your chosen duct size and airflow result in a velocity that is appropriate for the target environment.