Cfm And Duct Size Chart

Note also the return air grille sizing formula at the top of the chart.

Cfm and duct size chart.

This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Step three if desired airflow exceeds the cfm rating increase to the next duct size step four listed cfm is based on typical field results and may vary install dampers step five if duct run exceeds 25 or has excessive transitions increase to the next size step six design alone is inadequate always prove design by test and balance. Failure to do so will result in high velocity and very likely loss of airflow. Larger volumes or higher static pressures should be dealt with on an individual job basis.

For the same 2 5 ton system with a filter grille the grille size would need to be what size asked rick we usually use a 20 x 20 for 2 5 ton said the tech 20 x 20 x 2 800 800 cfm well that s big enough for a 2 ton but a 20 x 25 may be a better choice. Field duct sizing chart rectangular sheet metal duct 07 on most metal duct calculators duct size duct height net inside dimension in inches round duct size estimate. 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. The chart is based on metal duct.