ice on roof - how to thaw?

I've got a pathetically short little vent on the roof of my house that the upstairs bathroom fan is attached to. The house also has a very shallow pitch, so it collects a lot of snow rather than shedding it. It only takes 3 or 4 inches of snow cover to completely submerge the vent - this means its melting snow - which caused an ice dam and water to back up last year (our first year in the house).
so this year, i'm playing safe - have a ladder and roof rake at the ready on the deck so that if it snows any significant amount, I can clear an area around the vent so it doesn't cause another ice dam.
problem - my wife doesn't listen. on a few occaisions now we'd had notable snowfall - and yet she still used the fan in the morning. yes - I now have a buildup of ice downstream from the vent (which is about 4 feet from the eave of the house). there is a bare spot of about 12" round from her using it again this morning!! I'm now worried if we go much further with it, we'll for sure have another ice dam...
1. other than expensive and clumsy electric wire solutions, what can I use to perform a 1-time thawing of this ice buildup - just so it doesn't allow an ice dam to form? I was thinking about a chemical ice melter. I've seen them recommend it for roofs before....
2. there is such a thing as a much taller bathroom vent, right? what is a typical charge for a roofer to come in and replace the crappy small one with one of substantially more height? (I'd need one about 14" tall if possible) I'm looking for a ballpark so the roofer doesn't try and rip me off.
3. since the situation is much "after the fact", installing de-icing cables will be a pain, if not impossible. any other solutions to opening up the area right in front of the vent....in case wifey forgets /yet again/ ?
thanks for all the insight...
b
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Hamilton Audio wrote:

<SNIP>
For a quickie, one-time thaw, connect a garden hose to a hot water tap. All you need is a narrow channel melted to provide drainage.
Salt takes way too long to melt thick ice.
Jim
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I've used old pantyhose filled with salt. Makes a nice channel. IF you want a really fast melt, I agree with the garden hose squirting hot water.

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i've heard of the pantyhose thing with salt. I was just making sure that the product itself (chemical ice melter) will not harm the roof.
b

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wrote:

If you don't have pantyhoses, like most of us, try a sock. As for Salt, you might want to use on of those that are more lawn friendly, like magnesium cloride. So you don't kill the area around your down spouts.
hth,

Tom @ www.CarFleaMarket.com
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Hamilton Audio:

Send your wife up to chip off the ice, she won't forget next time.
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Hamilton Audio wrote:

Yep you screwed up, waited till winter. The solution is to just extend the pipe. Probably the cap just sits on top of the pipe (maybe a screw or two), so you can remove it, add an extension, and put it back on. You don't need more than a 12" extension. Even if the cap is part of the pipe, it wouldn't be hard to cut it off, put anew pipe over it screw it together and put a cap on that. Just don't fall off the roof or it will cost you a bundle.
OTOH. Turn the power off to the bathroom at the main panel. take the plate off the fan switch, pull the switch out, remove a wire and put a screw cap on it, put the switch back in the box and the plate on. When the wife says it doesn't work, just say Darn, will have to fix that in the spring.
If your wife really just forgets and isn't openly opposed to not using the fan, then just put tape over the switch in the off position.
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