1. What is Pressure Drop in Air Ducts?

Pressure drop refers to the loss of pressure as air moves through a duct system due to friction. It's a critical factor in HVAC system design and affects fan selection and energy efficiency.

2. How Does the Calculator Work?

The calculator uses the pressure drop formula:

Where:

• Friction Rate — Pressure loss per 100 feet of duct (inches water/100 ft)
• Length — Total length of ductwork (feet)

Explanation: The formula calculates total pressure drop by scaling the friction rate to the actual duct length.

3. Importance of Pressure Drop Calculation

Details: Proper pressure drop calculation ensures adequate airflow throughout the system, prevents excessive energy consumption, and helps select properly sized fans and equipment.

4. Using the Calculator

Tips: Enter friction rate (typically 0.08 to 0.15 inches water/100 ft for low velocity systems) and duct length. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical friction rate for HVAC ducts?
A: Most systems use 0.1 inches water per 100 feet, but this can vary based on system type and design requirements.

Q2: How does duct size affect pressure drop?
A: Larger ducts have lower pressure drop at the same airflow rate. Pressure drop increases exponentially as duct size decreases.

Q3: What's the maximum recommended pressure drop?
A: Total system pressure drop (including all components) should typically not exceed 1.5 inches water for residential systems.

Q4: Does this include fittings and elbows?
A: No, this calculates straight duct only. Additional calculations are needed for fittings, which typically add 30-50% to the total pressure drop.

Q5: How does air velocity affect pressure drop?
A: Pressure drop increases with the square of velocity, so higher velocity systems have significantly greater pressure drops.