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Vent hood -- placement of backdraft damper

Posted by attofarad (My Page) on
Sun, Apr 29, 12 at 16:38

I'm installing a Broan hood with a rooftop blower. The blower has a backdraft damper on its output, but Broan still indicates in the spec/instructions that one should be added inline.

The most convenient place for the damper would be immediately attached to the hood. For one thing, I could verify operation (and change spring if necessary, adjust, lube) by removing the hood baffles for direct access. The only reason I can think of for not putting it there would be if the flappers would result in more air turbulence noise if placed on the hood exit than if placed a bit further up the path.

Any experience with this?


Follow-Up Postings:

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RE: Vent hood -- placement of backdraft damper

Bump.

We just installed a custom hood with Broan PIK 45 and EB 15 external 1500 cfm blower. There clearly is still a bit of a draft. I'm going to talk to our contractor / HVAC guys tomorrow about installing this back-draft gizmo.

Any input or comments appreciated.

Will post updates.


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RE: Vent hood -- placement of backdraft damper

attofarad:

My hood has a damper just above it supplemental to the one on the output side of the roof fan. I don't think the hood damper adds significant noise, but a comparison test would be extremely inconvenient.

In any case, differential pressures due to wind gusts will cause some damper opening, so a pair of dampers provides additional resistance to air infiltration down the duct.

kas


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RE: Vent hood -- placement of backdraft damper

Thanks Kas, I will just add it right to the hood port.

Gary


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