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392 sq.inches versus 201 sq. inches?

mac_3
mac_3 Member Posts: 9
Hi Guys,

We have a warm air furnace retrofit job done for us by a sub. The challenge is the sub used a round duct connection on the return between two square duct sections.  It looks like the quantity of airflow will be substantially restricted compared to the supply side which does not have the reduction (restriction?).  The square inches of the square duct is 393 sq. inches.  The round flexible connector is 201 sq.inches.

The manufacturer (Rhhem) says the low heat airflow is 725 CFM @ 2" w.c. and high fire flows 900CFM @ 2"W.C..

Can anyone help me figure out if the reduction from hard duct to flex is a problem?  My opinion is we should change it becasue the customer wants us to.  The sub is asking for verificatiion there may be a problem.  I agree the unit is running but not sure of any issues that may develope from running it "restricted" over time.(?) 

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