I have a new home that was built to our local Green Home standards in Northern Canada. I installed 5 of these EcoVents by Broan based on the recommendation of my Green Home Ventilation advisor.
A picture and description is on page 6 here.
At 20$ a pop the vents are the most expensive I could have bought.
What I have now is 3 bathroom fans that will not exhaust (frozen ball), the dryer will only begin to exhaust after the warm air melts the frozen ice holding the ball in the cone (usually 5 to 10 minutes) and I have one vent for an unfinished bath in the basement that is free of ice and works when i tested it the other day (I suspect due to the fact that no moisture is ever present in the bathroom and the fan is never turned on).
Funny thing is, only one of the bathrooms is used for daily showering, the other 2 are used for toilet/sink only. So even with minimal moisture in the rooms and light fan use it is enough to cause freezing at the vent.
Now these were invented in Canada and I have have found some reviews online that state they are the best thing going, but to me they suck. They worked fine in the summer, but not worth a crap in the winter. The home has an HRV and the humidity is about 30 to 35% indoors. All vent ducting is 4 inch dia. with the last 10' wrapped in an insulated sleeve to help avoid condensation in the pipe. All bathfans are Panasonic FV-08VQ3. Runs are straight (no elbows) from fan to wall (about 15 to 20 feet).
If I can't come up with something to fix these things I'll be forced to remove them all next year and replace them with old school metal flappers.
I have tried running a fan overnight hoping that it will thaw the frozen ice, but to no avail. Only the dryer seems to be able to accomplish this due to the heat it puts out.
Sorry for being long winded, hoping someone else has dealt with these fans before.