How To Calculate Supply Air CFM

Supply Air CFM Formula:

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

Supply Air CFM:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Supply Air CFM Calculation?

The Supply Air CFM calculation determines the cubic feet per minute of air required to handle a specific heat load based on temperature difference. This is essential for HVAC system design and sizing to ensure proper heating and cooling capacity.

2. How Does the Calculator Work?

The calculator uses the CFM formula:

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

Where:

\( CFM \) — Cubic feet per minute (airflow)
\( BTU/h \) — British Thermal Units per hour (heat load)
\( \Delta T \) — Temperature difference in degrees Fahrenheit
\( 1.08 \) — Constant factor for standard air conditions

Explanation: The formula calculates the airflow required to transfer a specific amount of heat energy based on the temperature difference between supply and return air.

3. Importance of CFM Calculation

Details: Accurate CFM calculation is crucial for proper HVAC system design, ensuring adequate heating and cooling capacity, maintaining comfort levels, and optimizing energy efficiency in residential and commercial buildings.

4. Using the Calculator

Tips: Enter heat load in BTU/h and temperature difference in °F. Both values must be positive numbers. The temperature difference is typically the difference between supply air temperature and room air temperature.

5. Frequently Asked Questions (FAQ)

Q1: What does the 1.08 constant represent?
A: The 1.08 constant accounts for the specific heat of air (0.24 BTU/lb-°F) and air density (0.075 lb/ft³) at standard conditions, converted to minutes (60 min/hour).

Q2: What are typical CFM values for residential systems?
A: Typical residential systems range from 400-2000 CFM depending on home size, with about 1 CFM per square foot being a common rule of thumb for cooling.

Q3: How does altitude affect CFM calculations?
A: At higher altitudes, air density decreases, requiring adjustments to the constant factor. The 1.08 value is for sea level conditions.

Q4: What temperature difference should I use?
A: For cooling, use the difference between room temperature and supply air temperature (typically 15-20°F). For heating, use the difference between supply air and room temperature.

Q5: Can this formula be used for both heating and cooling?
A: Yes, the formula works for both heating and cooling applications, as it calculates the airflow required to transfer a specific amount of thermal energy.