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Do the joints in adjustable duct elbows need to be taped as well once they're adjusted or are they considered air-tight?

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what are you ducting? exhaust air from a bath fan or some type of combustion? Makes a big difference how you deal with it. – shirlock homes Oct 19 '12 at 10:48
It's a bathroom exhaust fan. – Brad Mace Oct 19 '12 at 11:56
Do you mean around the 3 joints in the pictured elbow? – Steven Oct 22 '12 at 3:03
up vote 7 down vote accepted

Do the joints in adjustable duct elbows need to be taped as well once they're adjusted

Yes, they do.

or are they considered air-tight?

No, they are not. Far from it, in fact.

You want to tape every seam in your ductwork, using (as Shirlock pointed out) foil tape. Each exposed seam, whether it's at a connection or part of pre-formed metal like the elbow in question, is a leak point.

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Do NOT use Duct or Duck tape as the backing for it degrades over time, faster with heat.

Edit: Even though this is for a bathroom fan, you still want to tape. Why? Because air leakage is moisture leakage, and you do not want to be pumping moisture into your attic. In winter it will lead to frost which will lead to mold.

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much better answer. Good job, as always. – shirlock homes Oct 19 '12 at 12:17

If you are ducting an exhaust fan from a bathroom or range hood, I would use an adhesive backed foil tape. Don't use regular duct tape on a range vent, clothes dryer or anything with higher heat.

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This really doesn't address the question that was asked. – The Evil Greebo Oct 19 '12 at 11:57

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