I am installing a new range hood for our kitchen. The duct exhaust at the top is 8" circular, but our old vent to outside is 10"x3.5" rectangular. I see what we could usually use a register boot but there is not enough space between the exhaust and the vent. The wall vent is just 1-2inches above the exhaust vent flange.

Is there a different HVAC part I could use? Could I build my own from metal or ductboard?


  • If you are saying there is only 1-2" to make the transition from round to rectangular, that is not enough room. About 6-8 inches is needed. Otherwise you are essentially reducing the duct to a 8X3 1/2" rectangular. Is this a wall or roof vent? – Jack Mar 17 '14 at 14:06
  • Thanks. It is a wall vent on a condo, so we cannot change it. We are looking at a company who can custom create a piece for us. – Simon P Mar 19 '14 at 14:57

We found an HVAC guy to build it from photos and measurements. With a bit of nudging, it went in after I cut the right whole in the box.


Probably there's better solutions, but I had to do something like this with a bathroom vent. I simply bought a roll of aluminum tape (used for ducts - not the plastic duct tape) and I built up three or 4 layers of connection between the two, essentially fabricating a bit of ductwork.

This is hidden in the ceiling so the look wasn't a big deal.

  • 1
    This is not the way that even a bath duct should be treated, although I am sure worse has happened. Kitchen hoods MUST be ducted in metal, or other approved material, securely fastened together, or should be, and joints taped to prevent leakage. – Jack Mar 17 '14 at 15:44

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