"J Kelly" wrote in message
...
On Mon, 14 Nov 2005 18:41:47 GMT, "Joseph Meehan"
wrote:

J Kelly wrote:
Last winter after a heavy snow I had a couple of problems with ice
dams. One above the exhaust hood over the stove, another above the
bathroom. Both appear to be caused by improper installation of the
fans, they both vent into the attic space. I'm going to correct this
by having them vent through the roof.

My question is this, wont the warm air coming out of those vents melt
the snow on the roof, and wont the resulting water end up freezing
into an ice dam as it tries to run down the cold roof where it runs
into more snow?

Yes, that is a classic case of irresponsible workmanship.

I think you misunderstood what I meant, rereading what I wrote I see I
wasn't very clear. After I correct the incorrect venting by
installing roof caps and running both exhaust fans to said roof caps,
won't the heat coming out of them when the fans are on cause the same
snow melting and ice dams that I get now by just leaving the vents in
the attic? Or will it just melt a little snow around the vent and
then the heat is able to escape before causing more melting? I'm in
northern Iowa, we can get some big snows.

Here's an interesting site concerning ice dams, lots of examples.

http://doityourself.com/waterproof/icedam.htm

If you are concerned that the warm air from the vents will melt the snow,
investigate insulated vents and/or higher stacks.