Can’t Get A Seal on Bathroom Exhaust – GreenBuildingAdvisor

Last year I added insulation to my attic (Twin Cities, MN) and replaced the bathroom exhaust fans and put in insulated hoses. I also air sealed all of the wall top plates and sealed up all of the attic bypasses.

Last week we had some extreme cold temps so I took a peek in the attic and found a fair amount of frost everywhere and I’m pretty sure the bathroom vents were the culprit.

This weekend I got back up there and redid the termination of the exhaust hoses and I feel like I sealed them up about as good as I can.

It’s not as cold now but still cold enough that frost is forming. The attached photo is from this morning after some of the kids got showers in their bathroom. Am I expecting too much by thinking I can completely seal it? Is there an acceptable amount of leakage?

I did the original work about a year ago so the previous vent leakage, being worse, still caused no mold to form as far as I can tell on closer inspection.