I think it's a tricky line between helping to keep room air from escaping, and hindering exhaust flow at startup and possibly running. The prevention of downdraft is obviously a good thing no matter what.
In any event, I wouldn't use one that had plastic involved, but stick to all metal, just in case.
he who throws mud loses ground -- this tiny ad is sitting on a lot of mud:
All of the video from the Eat Your Dirt Summit - more than 42 hours!
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