Cfm Flow Flexible Vent Vs Sheet Metal Ducting

I ve only been building since 1995 so i can t say for certain why we left the sheet metal guys behind but i suspect it was manly for cost reasons.

Cfm flow flexible vent vs sheet metal ducting.

Without it there would be tons more labor and material to make that final connection. I am not hating on metal pipe but flex duct is more practical in many applications. Flex duct allows easy connection from the main duct trunk to the hvac grille. The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe.

Like regular hvac duct flex duct work needs to be sized appropriately in order to flow the air volume which is measured in cubic feet per minute cfm correctly. Always stagger take off ducts by 12 to maintain pressure. Flexible ducts are fairly easy to install and will often cost less than the rigid ductwork. 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 duct size.

The table is based on the ducts friction loss formula. The rectangular dimensions and the air flow volume are adapted to the equal friction loss. I have seen many leaky metal ducts in crawl spaces as well. Flexible duct work must be stretched tightly for maximum air flow.

Flex ducts are better for existing trunk and branch heating and cooling systems. Use insulated duct or duct board in unheated spaces. In order to maintain velocity reduce duct size. The table below can be used to compare equivalent diameters for rectangular and round circular ducts.

Last take off run to be located 12 18 from end. Metal ducts are more rigid due to the nature of steel making them ideal to build an entire hvac system. Cfm 4 cfm 6 cfm 8 cfm 10 cfm 12 60 6x4 60 4x6 90 4x8 120 4x10 150 4x12. In this video i ll make a case for going back to rigid metal ducts for your trunk lines and keeping your flexable ducts to the last 10 or less of a.

Never locate ducts at the end of the trunk line run. This is because they re more versatile and flexible. Also i think spider webs are more likely to form in metal versus flex.