1. What is HVAC Air Flow Measurement?

Definition: This calculator determines the volume of air moving through an HVAC system in cubic feet per minute (CFM) based on air velocity and duct cross-sectional area.

Purpose: It helps HVAC technicians and engineers properly size and balance air distribution systems for optimal performance and efficiency.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q_{cfm} \) — Air flow rate (cubic feet per minute)
• \( V \) — Air velocity (feet per second)
• \( A \) — Cross-sectional area of duct (square feet)
• 60 — Conversion factor (seconds to minutes)

Explanation: The formula converts velocity in feet per second to volume flow in cubic feet per minute by multiplying by the duct area and time conversion factor.

3. Importance of Air Flow Measurement

Details: Proper air flow calculation ensures adequate ventilation, maintains comfort levels, optimizes energy efficiency, and prevents system strain.

4. Using the Calculator

Tips: Measure air velocity with an anemometer and duct dimensions to calculate area. Enter both values (must be > 0) to get CFM.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical air velocity in ducts?
A: Residential systems typically range 600-900 ft/min (10-15 ft/s), while commercial systems may be higher.

Q2: How do I measure duct area?
A: For rectangular ducts: width × height. For circular ducts: π × (radius)². Convert to square feet.

Q3: Why measure in CFM?
A: CFM (cubic feet per minute) is the standard unit for air flow measurement in HVAC systems.

Q4: What affects air flow accuracy?
A: Duct shape, surface roughness, bends, and obstructions can all impact actual flow rates.

Q5: How does this relate to tonnage?
A: 1 ton of cooling ≈ 400 CFM. This calculator helps verify if your ductwork supports your system's needs.