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I'm doing some remodeling in my house and would like to finish the basement ceiling with sheetrock replacing the old drop ceiling. The only problem is the ducts both run on one side of the room as illustrated in the picture. I'd like to reroute the return duct around the opposite side of the room so I can build a nice even soffit throughout the room.

Is it ok to reroute the return duct in such a way? Will adding additional length and two extra 90 degree bends to the duct cause any airflow problems or stress on the blower? What about reduced efficiency?

ducts

  • What are the duct cross sections? Would you have actual hard 90° turns, or would you have curved sections? – Daniel Griscom Jan 5 '17 at 1:03
  • @DanielGriscom, I would use a radius piece so it curved around the 90 degree bends. Not sure what you mean by cross sections, can you elaborate? I don't think a cross section of a hollow duct is what you are looking for. – Preston S Jan 5 '17 at 2:06
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    I was just curious how tall and wide each duct was. A large enough cross section, and the length won't really matter. A very narrow duct will cause problems. (I just thought that whomever answers this would like to know; I'm no expert in the field.) – Daniel Griscom Jan 5 '17 at 3:30
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    I never preferred a sheet rock ceiling in the basement. What if you need access above the ceiling to add or fix something? That said ,If all you are adding is a piece of straight duct and two elbows I see no reason to be concerned with duct sizing. The only time this would be a problem is if the existing duct is not large enough for the air flow now. I would have it checked by an HVAC company to make sure the existing duct is adequate for the airflow as it is now. Years ago, duct work was sized larger than it is today. Every one is trying to cut costs. – d.george Jan 5 '17 at 11:51
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    @JamesOlson, The duct is about 14" wide and the room is maybe 10 feet wide. That would make about 50% of the ceiling soffit in which case I would just put in the drop ceiling. – Preston S Jan 5 '17 at 15:01
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Yes, it's okay to reroute a 14" wide return air duct. Unlike the supply duct, the return air duct is passive (not dependent on the air velocity of a fan) to perform its function (the furnace won't be deprived of a lack of make-up air).

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    What!!! The return air duct , being on the negative side of the fan/blower , should have a lower resistance factor and thus be slightly larger than the supply duct to reduce air noise. – d.george Jan 5 '17 at 19:26
  • @ d.george air noise is not a factor in this situation; therefore the return duct may remain the size it's always been despite the proposed configuration. – James Olson Jan 6 '17 at 2:43
  • The air noise would be a factor if you were living in this house. It is definitely a factor in my house – d.george Jan 6 '17 at 10:48
  • I spoke with a professional HVAC tech and they agreed that I could reroute the duct. Although I do not agree with your statement that the furnace will not be affected by changes to the return duct. Increasing trunk length and adding bends will increase resistance on the blower but in this case it was minimal. – Preston S Mar 2 '17 at 19:10

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