Damper for kitchen ventilator

The external damper for my kitchen stuck open last month. It's not frozen shut, but I can't get up to it until spring. I now have quite an effective reverse chimney into my kitchen. I have a choice of using the vent fan or packing it full of towels (I'd refer to have the vent available for use). The vent pipe runs up thru the ceiling behind a cover and is easy to get to. Any suggestions for installing a flapper in the kitchen? I'm thinking a powered damper might be best as the old one was never that effective at sealing and every time the wind blows, you hear it flapping around.
Recommendations for a good soluntion? The powered dampers I've seen online don't look like they are designed to seal well (they are intended for chimney flues). -------------------------------------
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On Feb 8, 11:49pm, gpser_at_hotmail_dot snipped-for-privacy@foo.com (AlH) wrote:

Most dampers are in the fan housing.
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