Flex Duct Cfm Ratings Chart

On a slide rule duct calculator i have it states that a 9 inch flex duct is rated at about 205.

Flex duct cfm ratings chart.

Duct system sizes and airflow quick chart created date. The flex duct size may be different than the hard duct that runs to that room. Flex duct 05 on most metal duct calculator round metal pipe 06 on most metal duct calculators field duct sizing chart rectangular sheet metal duct 07 on most metal duct calculators step one identify the volume of air that will be passing through the duct step two select the duct size from the table that can carry that volume of air step three if desired airflow exceeds the cfm rating increase to the next duct size. In the following chart.

Larger volumes or higher static pressures should be dealt with on an individual job basis. Flex duct 05 on most metal duct calculator round metal pipe 06 on most metal duct calculators field duct sizing chart rectangular sheet metal duct 07 on most metal duct calculators. Air volume equivalent round air volume cfm 4 6 8 10 12 duct inches cfm 50 6 x 4 550 75 6 x 4 675 100 8 x 4 6 x. Input the required cfm in the box below that.

Failure to do so will result in high velocity and very likely loss of airflow. 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. Shr 80 to 85 19º td ave. Digitalplumber is just a name for use here i am not a plumber.

The chart is based on metal duct. Select the duct type on the pull down menu. Click calculate and you will see the size of flex duct you need for that room. Flex duct has a higher pressure drop and as such may require the size shown on this guide be increased by 1 round size for up to 800 cfm and 2 round sizes above 800 cfm to insure proper airflow.

This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.