1. What is the CFM Duct Pressure Equation?

The CFM (Cubic Feet Per Minute) equation calculates airflow from duct pressure measurements. It provides an accurate assessment of air volume flow in HVAC systems based on area and velocity pressure.

2. How Does the Calculator Work?

The calculator uses the CFM equation:

Where:

• \( A \) — Area (ft²)
• \( VP \) — Velocity Pressure (in WG)

Explanation: The equation calculates airflow volume based on duct cross-sectional area and the square root of velocity pressure, with 4005 being a constant conversion factor.

3. Importance of CFM Calculation

Details: Accurate CFM calculation is crucial for proper HVAC system design, balancing air distribution, ensuring adequate ventilation, and optimizing energy efficiency in building systems.

4. Using the Calculator

Tips: Enter area in square feet, velocity pressure in inches water gauge. All values must be valid (area > 0, VP > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is velocity pressure in HVAC systems?
A: Velocity pressure is the pressure created by air movement in the duct, measured in inches of water gauge (in WG), which represents the kinetic energy of the airflow.

Q2: Why is 4005 used as the constant?
A: The constant 4005 incorporates conversion factors for units and accounts for standard air density conditions (0.075 lb/ft³ at 70°F).

Q3: What are typical CFM values for residential systems?
A: Residential HVAC systems typically range from 800-2000 CFM, depending on the size of the home and system capacity.

Q4: When should velocity pressure be measured?
A: Velocity pressure should be measured when the system is operating at design conditions, with all dampers in their normal operating positions.

Q5: Are there limitations to this equation?
A: This equation assumes standard air density and may need adjustment for high-altitude locations or non-standard air conditions.