1. What is the HVAC Air Flow Calculation?

Definition: This calculator determines the required air flow rate (CFM) for an HVAC system based on the cooling load and temperature difference.

Purpose: It helps HVAC professionals and engineers properly size ductwork and select equipment for optimal system performance.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q_{cfm} \) — Air flow rate (cubic feet per minute)
• \( Q_{btu} \) — Cooling load (British Thermal Units per hour)
• \( \Delta T \) — Temperature difference between supply and return air (°F)
• 1.08 — Constant combining air density and specific heat

Explanation: The formula converts cooling capacity to air flow rate based on the system's ability to remove heat from the air.

3. Importance of Proper Air Flow Calculation

Details: Correct air flow ensures efficient system operation, proper humidity control, even temperature distribution, and energy efficiency.

4. Using the Calculator

Tips: Enter the cooling load in BTU/h and temperature difference in °F (default 20°F). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical ΔT for residential systems?
A: Most residential systems use 18-22°F difference between supply and return air.

Q2: Where does the 1.08 constant come from?
A: It's derived from the product of air density (0.075 lb/ft³) and specific heat (0.24 BTU/lb-°F) × 60 min/hour.

Q3: How do I find my cooling load (Q_btu)?
A: Use Manual J calculations, rule-of-thumb estimates, or professional load calculation software.

Q4: Does this work for heating calculations?
A: Yes, but ensure you're using the correct ΔT for heating mode (typically smaller than cooling ΔT).

Q5: What if my system has variable air flow?
A: This calculation gives the maximum CFM needed at peak load conditions.