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modifying bath fan vent duct size

Barshfield's picture

I am replacing my bath fan.  The outlet of the fan is nominal 4:" (actual 3.75") and the vent duct to which it is supposed to connect is nominal 3.5" (actual 3.25").  Do I 1) get an adapter of some sort (and, if so, where)?  2) slice up the end of the duct to fit over the fan outlet and then use more duct tape than it would otherwise deserve? or 3) do something else?  Thanks, Mark

If possible find an adapter, (post #207795, reply #1 of 6)

If possible find an adapter, but with the expanding aluminum (almost foil) duct material it's fairly easy to "gather" the duct arond a smaller one, with a "hose clamp".


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

the duct is smaller than the (post #207795, reply #2 of 6)

the duct is smaller than the outlet of the fan, which means I need to expand the duct or find an adapter. Or something else.  I'm reluctant to go slicing into the flexible duct, just to make it bigger to surround the outlet.  But that might be my first and best shot at it.

I was thinking a short piece (post #207795, reply #3 of 6)

I was thinking a short piece of the expandable stuff in the larger size, scrunched down on one end.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Barsh (post #207795, reply #4 of 6)

There is available in most places that sell fans, a plastic reducer fitting.

or

An HVAC supply should be able to give you one in galvanized.

They'll call it a 4 to 3", but it will allow you to fit over it.  I'd use the alum. foil tape for all connections.  Peel and stick paper backing, also available from the above suppliers.

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Get the other Fan (post #207795, reply #5 of 6)

As you explained that your duct is smaller than fan so in my opinion you should expand the duct and if you cannot do so get the smaller fan for duct because no other option is there.

Mt (post #207795, reply #6 of 6)

You'd best read the thread again.

It's not my fan.

There is another option w/o replacing the fan-4" to 3" reducer.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/