HVAC Duct CFM Calculator

HVAC Duct CFM Calculator

HVAC Duct CFM Calculator

Calculate The CFM For Your HVAC Duct And Size Your Systems Properly To Ensure Efficient Heating, Cooling, And Space Ventilation!

Use our free HVAC Duct CFM Calculator above and calculate your system’s airflow capacity Effortlessly.

What Is An HVAC Duct CFM Calculator?

An HVAC Duct CFM calculator helps you calculate the cubic flow per minute of your ducts and determine the airflow capacity of the system. Calculating the CFM will give you the volume of air flowing through the duct per minute.

Why Are HVAC Duct CFM Calculations Important?

HVAC Duct CFM calculations are essential to determining the correct amount of air for each room. These calculations ensure that your system runs efficiently and minimizes the amount of energy wasted due to incorrect duct measurements. They also enable a comfortable room environment and effective cooling and heating of your space.

How To Calculate CFM of Your HVAC Duct?

Our HVAC CFM Duct Calculator accurately measures the volume of air passing through your ducts. It is pretty simple to use. All you need to do is have some data ready for a faster process. 

What Data Do You Need To Keep Ready Beforehand?

Friction Loss Rate: This refers to the amount of pressure lost per unit length of the duct.

Total Equivalent Length: This refers to the total size of the ductwork system. 

Duct Type: This refers to the material used for the ductwork. You have two options – metal and flexible. 

Duct Shape: This refers to the shape of your ductwork. It could be circular or rectangular. 

Calculation Type: This is where you select whether you need to calculate the CFM or the diameter of your duct system. 

Diameter: this refers to the diameter of your duct. 

Side One and Side Two: These are the length and width of your duct, and they are relevant if the duct is rectangular or square. 

Number of 45-degree Bends: This refers to the frequency of 45-degree bends in your ductwork. These bends create additional airflow resistance, which can lead to pressure loss. 

Number of 90-degree Bends: This refers to the frequency of 90-degree bends in your ductwork and causes more significant airflow issues. 

Number of 180-degree Bends: This refers to the frequency of 180-degree bends, also called U-turns, in your ductwork system. Try to minimize these bends, as they can cause significant pressure loss. 

The Calculation Formula

The formula for calculating the CFM of your duct is = Velocity x Area. 

To find the velocity, multiply the pressure drop by two and multiply the friction factor and density of air separately. 

Now divide both the results and find the square root of it.

The formula for finding the velocity

√(2 x pressure drop/ friction factor x density of air ) lb/ft3 

To find the area, multiply both sides of the duct or divide the diameter by 2, depending on the shape of your duct. 

Now, calculate the CFM easily by multiplying the velocity by area.

How To Calculate The Diameter Of Your Duct System?

With our HVAC Duct CFM Calculator, you can also calculate the diameter of your duct system. 

Just select the diameter option from the drop-down menu when you click on the ‘Calculation Type.’ 

The Calculation Formula

To find the diameter, use this formula: 

If circular: (CFM X 4)/ π X Velocity 

If rectangular: area/side 1. To find the area, the formula is CFM/Velocity

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