Double dampers on bathroom exhaust fan
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| Posted in General Questions on
We have already installed the bathroom exhaust fan’s, and they have their own backdraft damper towards the actual bathroom side.
We are using hard metal ducts, insulating them, and exiting them through the bird box soffit which extends out 5 feet from the closest vented soffit.
I want to make sure the duct extends through the soffit, and plan on using the Duraflo model suggested by Martin. This also has a backdraft damper.
Is two dampers too much? I don’t want to over think it, but would I be causing any air to become trapped between the two?
We have installed timers which automatically run the fans for 30 minutes.
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Replies
Bridget,
Don't worry -- the fan should be able to handle two backdraft dampers.
That said, any duct system introduces static pressure (reducing cfm). A straight 6-inch duct with no elbows has significantly less static pressure than a 4-inch duct with two or three elbows. The smaller the diameter of the duct, and the more elbows, the greater the static pressure. Lots of builders discover (too late) that their poorly designed duct system has hurt the performance of their bathroom exhaust fan.
-- Martin Holladay
What is the Duroflo model that Martin suggested? A search does not return anything on it.