Trouble connecting 4 inch fan to 5 inch duct.


Old 01-07-12, 06:09 PM
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Trouble connecting 4 inch fan to 5 inch duct.

I am trying to replace a new bathroom fan. I purchased the Air King BFQ70. My old fan had a 3 inch opening. The builder used an adaptor to attach it to the 5 inch duct.

My new fan has a 4 inch PVC opening. I went to pick up an adaptor but when I tried to attach it, I couldn't fit the end over or under the fan opening. (The other end fit fine over the duct).

I went back to the store and realized there are increasers and decreasers. What is the difference and which one will fit on my fan or is there something else I should be trying?

Thank you for your advice.
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Old 01-08-12, 03:57 AM
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An increaser will fit "over" your fan outlet and inside the duct. A decreaser will fit "over" the duct and inside the fan outlet. You want an increaser, although you may not find one that fits inside the duct. You'll be taping both joints with metal tape anyway, and you won't notice the turbulence caused by the fitting.
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