# How large should my furnace intake duct be?



## landbug (Aug 9, 2010)

I have a 2500 sq/ft single story home.  I want to install a new furnace-AC unit.  The system I want to install is a Rheem 125K BTU Furnace. My current intake (return) duct measures 7" X 20".  According to my calculations, I'm supposed to be able to move 1560 CFM (for a 125K BTU furnace.)  Will the 7" X 20" duct handle this?  If not, then what size should I consider?


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