# How do you calculate flexible duct size?

## How do you calculate flexible duct size?

Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room. For example, a 10-by-10 room will be 100 square feet.

### How many CFM do I need for flex duct?

CFM Sizing Chart For Flex Round Ducts (50-1,700 CFM)

Duct Size (Inches) Flex Duct Airflow (CFM)
10 inches 300 CFM
12 inches 480 CFM
14 inches 700 CFM
16 inches 1,000 CFM

#### How do I know what size duct to use?

b. The size of your duct work depends not just on the size of your entire house but also on the size of each individual room. Thus, one needs to gauge the square footage of the entire house as well as that of all the different rooms in order to decide duct work sizing.

How many CFM can a 12 inch duct handle?

715 cfm
The rule of thumb for a 12 inch duct is 715 cfm. You would need a 20 inch duct to handle 2000 cfm.

What happens if ductwork is oversized?

Using oversized ducts will erode the system’s efficiency, while undersized ducts won’t carry the necessary volume of air. Balanced airflow. To maintain neutral pressure in the HVAC system and throughout the house, the duct system must deliver and return a matching volume of air.

## What size duct do I need for a 2.5 ton AC unit?

For instance a 2.5 ton system (Approximately 400 CFM per ton) would require (2) 14” flexible return ducts or (1) very short flexible 18” duct to move the 1000 CFM required by the 2.5 ton system.

### What is the formula for duct sizing?

Measure the distance across the duct, in inches, then multiply by 3.14159 if the duct is circular to find its circumference, in inches. Then, measure the length of the duct–in inches–and multiply by the circumference. This is the number of square inches in the duct area. Divide by 144 to determine how many square feet are in the duct area.

#### How to calculate residential duct size?

How To Calculate The Duct Size Look on your furnace to see how many BTUs (British Thermal Unit) it produces. This information is usually given on the furnace plate. Multiply the answer by the Cubic Feet per Minute (CFM) airflow of your furnace. Divide the answer you get in step 2 by 10. Now calculate the duct size by multiplying the length with width.

How do you calculate the CFM of a duct?

Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room. For example, a 10-by-10 room will be 100 square feet. Figure out the amount of CFM that is required for the room. Properly ventilated homes use 1 CFM per square foot of space.

How do you calculate duct size with area given?

Measure the square footage of each room in the house. This is done by multiplying the width by the length.

• Calculate the cubic feet per minute (CFM) that is needed for each room. This is how to measure airflow.
• Calculate the duct size by using a duct calculator.
• Determine the cubic feet per minute and duct sizes for all the rooms.