I verified that what I have in my half bath is a NuTone 8870. The flap on the vent is not closing tightly, and cold air is flowing through there. I am not sure if they were added, or original, but there are some foam strips that the door is supposed to close against, but isn’t. I pulled the fan motor, and blades out of the duct, and shoved a plastic bag full of insulation into the duct. So at least the cold air is stopped. I debated about whether to buy another Nutone 8870, or a Panasonic WhisperWall 70 FV-08WQ1. I also considered a couple others, but not seriously. I looked at the Broan 512m, but the duct diameter is 6″, where I have a 7 1/8″ hole in my wall. That would leave a serious gap. The WhisperWall 70 has a 8″ diameter duct, but it will be easy to cut the hole a little bigger. The WhisperWall 70 cost twice as much as the 8870, but the appearance is nicer, it is quieter, it is Energy Star approved. But the big thing is that it mentions a damper with a foam seal, where the specs for 8870 don’t mention a foam seal.
With the bag of insulation stuffed into the cavity of the old fan, thus blocking the flow of cold air, I will probably wait until spring to install the new fan.