How to Calculate CFM HVAC

CFM Formula:

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

Cubic Feet per Minute (CFM):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is CFM in HVAC?

CFM (Cubic Feet per Minute) is a measurement of airflow volume in HVAC systems. It represents the amount of air that flows through a space in one minute and is crucial for proper heating, ventilation, and air conditioning system design and operation.

2. How Does the Calculator Work?

The calculator uses the CFM formula:

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

Where:

\( BTU/hr \) — Heating or cooling load in British Thermal Units per hour
\( 1.08 \) — Constant factor for air density and specific heat
\( \Delta T \) — Temperature difference in degrees Fahrenheit
\( CFM \) — Cubic Feet per Minute airflow

Explanation: The formula calculates the required airflow to transfer a specific amount of heat energy given a temperature difference, accounting for the properties of air.

3. Importance of CFM Calculation

Details: Accurate CFM calculation is essential for proper HVAC system sizing, ensuring adequate airflow for heating and cooling, maintaining indoor air quality, and optimizing energy efficiency.

4. Using the Calculator

Tips: Enter BTU/hr (heating or cooling load) and temperature difference in °F. Both values must be positive numbers. The calculator will determine the required CFM for your HVAC system.

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), combined to simplify calculations.

Q2: What are typical CFM requirements for residential HVAC?
A: Typical residential systems require 350-400 CFM per ton of cooling capacity, but this varies based on system design and building characteristics.

Q3: How does CFM affect HVAC system performance?
A: Proper CFM ensures efficient heat transfer, prevents coil freezing, maintains comfort levels, and extends equipment lifespan. Incorrect CFM can cause poor performance and higher energy costs.

Q4: When should CFM calculations be performed?
A: CFM calculations should be done during HVAC system design, when replacing equipment, when modifying ductwork, or when troubleshooting comfort or efficiency issues.

Q5: Are there limitations to this calculation method?
A: This method provides a basic calculation. For complex systems, factors like altitude, humidity, duct losses, and specific application requirements may need additional consideration.