On Friday, December 7, 2018 at 8:14:06 AM UTC-5, Linda wrote:
replying to Charles Spitzer, Linda wrote:
I have a jenn air flapper on the outside of my house with a screen back some
distance so small animals cannot get inside the crawl space. It has been
checked by the installer twice and said to be ok. I think cardboard or
insulation needs to be put where air comes in from the outside of this flapper
in back of. Maybe cardboard here.? I know a folded up piece of cloth does
not help- not warm.

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You can check it yourself, see if the flap swings freely. Gluing a small
weight, like a nut to the bottom may help keep it closed. Just make sure
it still opens when the blower is on.