In remodeling my bathroom I had to convert a 6"x6" square duct underneath the floor joists in the basement to flex so I can get around my new toiler drain. I cannot for the life of me find a 6"x6" square to 6" round transition anywhere.

Do I need to fabricate one myself? I don't know what to do.

I am aware that a 6" round duct is smaller than 6"x6" square by ~20%. It feeds the foyer which I have kept the damper nearly closed anyways because it gets very hot/cold in that location.


2 Answers 2


They do exist. Best bet is probably to contact a local sheet metal shop, if they don't have one they can build one. Expect this to cost in the tens of dollars range.

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You could potentially cap the end, and then use a round duct takeoff. The downside is it will restrict flow to the vent because of the abrupt end and sharp angles internally.

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There's another type of side takeoff that is rectangular, and if you can find one you could potentially modify it yourself using a couple strategic cuts and copious amounts of foil tape.

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  • I agree that contacting a local shop might be a good solution. It's not a very complicated or uncommon part for a shop (the sizes might throw them off slightly).
    – JMac
    Feb 22, 2017 at 19:28
  • Called a local shop and he has a 6x6x6 ceiling box that he said should do the job, I'm going to swing by today and pick it up. Thanks for the advice! Feb 23, 2017 at 17:18

You'd just cap the square duct and install a takeoff in the cap. It may be difficult to find a hemmed end cap in 6x6, but as you can imagine it would be trivial to fabricate a simple wraparound cap.

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