Stove hood fan making noise when windy... normal?

curls00

Hey everyone.

We have a hood fan in our kitchen that, when it's windy outside, we hear what we think is either something loose or something knocking. Sounds somewhat tinny, so I think it's a fan blade or something along those lines.

Is this normal with most hood fans? It's a cheaper unit (Broan) and not one of the ones with the fan itself mounted in the attic. If there's something I can adjust or fix to solve this, what is it?

Cheers.
Eric

jbfan

Does it vent out the side wall? It may be a flapper valve that is moving with the wind, or whatever that thing is called to keep animals out when the fans is not running.
If it were the blades, you would hear it when it was running.

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curls00

Fairly sure it vents out the roof, as the wall it's nearest is a common wall with the neighbour of my townhome. Although tomorrow I'll look out the back door to see if maybe it vents out the rear of the house, although I don't recall that being the case.

End Grain

Sounds like jbfan hit it on the head, i.e. the metal closure flap in the duct is bouncing with the wind.

curls00

OK, sounds logical. Now, is it normal? And can it be minimized?

redline

Turn the "flapper" in the opposite direction so as the wind will not activate it.

troubleseeker

Must be missing something here. The "flapper" everyone keeps referring to is nornally located directly between the hood and the first piece of connected duct work. It cannot be reversed because then it will not open when the fan is turned on, and in most installations it is not accessable anyway without disconnecting the hood.

Unfortunately most of them are extremely light, flimsy pieces of aluminum and wind blowing across the end of the duct work often causes them to chatter, especially in short straight runs of duct.. They are intended to keep wind from blowing down the pipe into the house, but mostly they are a nuisance.

Ron6519

There are two flappers. One as it exits the fan and the other at the roof exit. They cannot be turned or adjusted. You will hear them on windy days.
Ron