392 sq.inches versus 201 sq. inches?

mac_3

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.(?) 

alotlikeearl

Flex Diameter

I'm too lazy to do the math.  What is the size (diameter) of the flex?  Does the furnac have an A/C unit attached?  If so, what is the tonnage? 

Techman

Air Flow

You are going from 20" x 20" to 16"round . Is the round duct ,flex duct? How long? Straight run or turns in the round duct? As above, more info is needed, Rheem mn#, AC?What size is the supply trunk?  Maybe the round is the correct size and the square is slightly oversized ? Temp rise across the UNIT ,not temp rise from return grill to supply register.?

icesailor

Square pipe in a round hole:

This sounds like a good question for hvac-talk. Any pictures?

www.hvac.talk.com

Jean-David Beyer

square holes?

Here is a video of a machine drilling square holes in metal. In Japanese, but that does not matter.



https://www.youtube.com/watch?v=tqOe2In9ShQ



https://www.youtube.com/watch?v=L5AzbDJ7KYI&feature=related