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How Attic Air Ducts May Cause Ice Dams

If you have an older home, you might have a glaring problem that causes ice dams. Years ago, many builders ran duct work and vent lines through the attic.  It seems they didn’t consider how that might affect homeowners down the line.

Those vents and ducts often are under-insulated (or not insulated at all) and poorly sealed.  As you run your furnace, your ducts in the already-hot attic act as heating coils.  The result is an attic that’s even hotter than usual.  The hotter the air under the shingles, the more likely it is an ice dam will form.  You want a cooler attic.

You should be concerned about duct work or air-vent lines in your attic even if they appear insulated.  Often, these lines will have some insulation but it will not be enough insulation to keep your attic from unnecessarily warming up.

Air handlers are another problem you might find in your attic.  Air handlers often create the unintended effect of letting excess heat flow from your living space into your attic. The joints in the air handler cabinets usually aren’t sealed very well, either, especially if it’s an older model.  Another way to heat up your attic, and another way to invite ice dams.

To see how this can make heat start to pour into the attic (and to see how energy-efficiency professionals handle these problems) check out the video below:


In the video, the guy talking about cooling the, not heating it up, but the principle is the same: When you run heat through the house, you’re also blasting heat through the thermally leaky areas.

If you’re seeing a lot of ice dams in the winter and you keep your home relatively cool, go up into the attic for a moment and look for any ductwork or vent lines.  If you see them, call a home energy professional to get an audit (similar to the one done in the video).  You probably can’t reroute all the duct lines, but you can get superior insulation that may lessen the amount of heat they add to your attic.

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