6" duct bathroom exhaust fan

OK this is probably a really stupid question but I thought I ask...
I would like to get a high power exhaust fan for my bath. Most of them use 6" duct to vent to the roof. My roof vent is 4" and I don't want to change it.
Can I get a fan for 6" and then use a reducer to go from 6" to 4" duct then to the vent?
Will this make it work "better" than a regular 4" exhaust fan?
I think this is a bad idea...
MC
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MiamiCuse wrote:

It'll work, but it might be noisier and pull a little less air than it would with a 6" vent. Whether you'll get better performance than from a smaller fan designed for a 4" vent, I don't know.
nate
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MiamiCuse wrote:

Depends. You might get better performance for awhile. Then, because the fan is having to work harder due to the restriction in the duct, you can make the decision again when you have to replace it because it burns up.
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Robert Allison
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Ideally one should use 6" duct all the way (including roof vent) for a fan with a 6" outlet.
A 6" to 4" reducer will add "effective length" to your duct run as will your 4" roof vent.
Before you go through all the added complication of dealing with using 6" fan on a restricted ducting system...how about looking into an adequate fan (cfm & noise level) that is designed to work with a 4" duct?
Depending on the size of the bathroom & moisture loading, a 4" fan could work just fine.
Over sizing the fan wrt to cfm is not necessarily a good thing.
cheers Bob
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Me too. Consider
http://www.sunfrost.com/efficient_shower.html
Nick
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