Hmmm, that's interesting. We have a fan unit in the attic that vents 2 bathrooms that are side by side. From the unit, the vent duct goes straight up to the roof.

You could certainly insulate the duct work, I am pretty sure we did that mostly for noise (we used rigid ducts and you hear the turbulence, not the fan). We have a cathedral type ceiling in both bathrooms, and we mounted the vent on the vertical wall above the shower head, routed to the motor, then as above (does that make sense to you?). This does not eliminate the heat loss into the duct, but as it is on a vertical wall, rather than the ceiling, maybe it is less like a "chimney", although I am sure we loose heat there too.

This routing avoids running what sounds like a "heat conduit" between the roof and ceiling.

But now I think I will go outside in the morning and look at our roof after over a foot of snow...

Thanks for your reply. It is somewhat heartening to know there may be a ceiling exhaust option.

Our bath fan IS in the bathroom ceiling and there really is no "duct work" at all. It is simply mounted into a framed out area between two joists. The spiral, flexible tubing connects right to the fan housing and this tubing is squished between the sheetrock sloping ceiling and the bat of insulation all the way down to the soffit...a distance of at least 5'. Since it compacts the insulation this tends to decrease the insulation R value.

I was wondering how a vertical exhaust fan through the roof would deal with a thick layer of snow above. We are in NH and have had several storms already. I e-mailed on on-line bath fan dealer to see what they have to offer but no answer yet.

OK, so I didn't make it into the backyard to look up at the roof today- left for work in the dark, home after work in the dark.... that's changing soon, right??

We have been using it since the last storm (meaning we have showered since then!!), and there is about a foot of snow, even the skylights are still covered (gee that glass is well insulated!). The bathroom cleared out completely this morning when I took my typical steamy shower, so...

We are working on the adjacent bath tomorrow, so I will update you. I know I looked at a Panasonic unit, but hubby went and bought something else before we consulted, but it was essentially the same.

Here is a link that might be useful: Panasonic In-line vents

Well, what we have on the roof is a spring loaded damper. It sort of upsidedown U shaped. I can imagine that it could get blocked with lots of snow, although that has not happened here to date, but NW Jersey is not quite the same as NH- you get lots more snow. Hubby and I were contemplating this today, but it has functioned well in the face of about 15" of snow.

Soooo....