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 heat load and temperature difference.

Purpose: It helps HVAC professionals and engineers properly size ductwork and select appropriate equipment for heating and cooling systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The formula calculates how much air flow is needed to transfer the specified amount of heat given the temperature difference.

3. Importance of Proper Air Flow Calculation

Details: Correct air flow ensures efficient system operation, proper temperature control, and prevents equipment strain or short cycling.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What's a typical ΔT for HVAC systems?
A: Residential systems typically use 15-20°F, while commercial systems may use 20-30°F differences.

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), converted to minutes.

Q3: How do I find the heat load (Q_btu)?
A: Use a Manual J calculation or our Heat Load Calculator tool for accurate BTU requirements.

Q4: Does this work for both heating and cooling?
A: Yes, but cooling systems often have additional factors like latent heat to consider.

Q5: What if my system uses metric units?
A: Convert inputs: 1 kW = 3412 BTU/h, °C to °F conversion needed for temperature difference.