How To Calculate CFM In HVAC System

HVAC Airflow Formula:

\[ CFM = \frac{BTU/hr \times 1.08}{\Delta T} \]

CFM (ft³/min):

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1. What Is CFM In HVAC Systems?

CFM (Cubic Feet per Minute) measures airflow volume in HVAC systems. It represents the amount of air moving through the system per minute and is crucial for proper heating, ventilation, and air conditioning performance.

2. How Does The Calculator Work?

The calculator uses the HVAC airflow formula:

\[ CFM = \frac{BTU/hr \times 1.08}{\Delta T} \]

Where:

\( CFM \) — Cubic Feet per Minute (ft³/min)
\( BTU/hr \) — British Thermal Units per hour
\( \Delta T \) — Temperature difference in degrees Fahrenheit (°F)
\( 1.08 \) — Constant factor for air density and specific heat

Explanation: The formula calculates the required airflow based on the heating/cooling load (BTU/hr) and the temperature difference the system needs to achieve.

3. Importance Of CFM Calculation

Details: Proper CFM calculation ensures efficient HVAC operation, adequate air distribution, optimal energy consumption, and prevents issues like hot/cold spots or excessive noise.

4. Using The Calculator

Tips: Enter BTU/hr (heating or cooling capacity) and temperature difference in °F. Both values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is the 1.08 constant in the formula?
A: The 1.08 constant accounts for the density of air (0.075 lb/ft³) and the specific heat of air (0.24 BTU/lb°F), converting BTU/hr to CFM.

Q2: What is a typical CFM range for residential HVAC?
A: Residential systems typically range from 400-2000 CFM depending on home size, with 1 CFM per square foot being a common rule of thumb.

Q3: How does CFM affect system performance?
A: Too low CFM reduces heating/cooling capacity and efficiency; too high CFM increases noise and may reduce dehumidification in cooling mode.

Q4: Can this formula be used for both heating and cooling?
A: Yes, the formula works for both heating and cooling calculations, using the appropriate BTU/hr and temperature difference values.

Q5: What factors affect actual CFM requirements?
A: Duct design, static pressure, air density at altitude, and specific application requirements can all affect actual CFM needs.