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Maximum number of bends in new AC duct work


I am currently retrofitting an apartment with central AC. My HVAC contractor has installed the furnace and the duct work, but I am concerned about how the ducts run:
One duct has two 45 degree bends and three 90 degree bends, another has five 90 degree bends, two right next to each other, basically forming a U. The total length of each duct is under 20 ft, hooked up to a 2 ton unit (there are also two smaller ducts, less than 4 ft each). I think it's possible without too much effort now to reroute the ducting to eliminate two-three 90 degree bends from each duct.

My question is whether the bends will negatively affect cooling efficiency. Is there a maximum number of bends that can be put into a duct? Should I have him reroute the ducts to minimize the number of turns?

Thanks for your input,


Re: Maximum number of bends in new AC duct work

Sure sounds like a messy installation.
From what I understand every 90 degree adds restriction to air flow equivelant to about 6 feet of extra length. The U shape is really going to slow down the air flow.

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