# Duct static pressure question



## engineer (Aug 21, 2011)

I'm not a duct expert (my primary field is indoor air quality) so here goes...

3 ton Carrier Infinity packaged unit model 50XT going into existing duct system with 10 x 20 main ducts. The static pressure is 0.1 in the supply and 0.42 inches in the return, so 0.52 is the total static pressure measured in the ducts about 6 inches form the unit flanges. (The return has two right angle bends which are rectangular turns with a pinch down to 8 X 18 where the ducts are mated-the original installer just cut a hole an inch less than the size of the duct and didn't seem to care (or know) that he was creating a turbulence inducing "pinching orifice"!).

Carriers product info shows the same airflow from 0.1 to 1.0 total static pressure. So should I worry about this? Even though its ugly it seems to be within the operating specs, at least roughly in the middle of their chart.

I can desribe the return as follows: 25x25 filter mounted vertically on a 10 x20 that drops down 4 feet then mates into a horizontal 10 x 20 (with the 10 inch side mounted into the 20 inch side!) that goes just a few inches and then makes a 90 degree turn into the main return duct also 10 x 20 and runs horizontally straight into the unit's return flange.

Can anything be done to improve the flow short of ripping it out? (Soffits etc are involved) Or is it OK as is?


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