Ice Buildup On Furnace Flue Cap


Old 01-14-17, 04:38 AM
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Ice Buildup On Furnace Flue Cap

Hi everyone.

This is my first winter in this house, so I'm discovering new things as time goes by. As I was backing out of my driveway the other day I noticed some ice buildup on and around the furnace flue cap. With a big hunk of ice on the roof that had most likely dropped from the furnace flue cap area.

This is my feeble attempt at making a drawing of what the ice buildup looks like.

Name:  ROOF ICE.jpg
Views: 3292
Size:  14.3 KB

Is this something I need to be worried about ?? Is there the possibility that the furnace flue is installed incorrectly ??

The furnace was put in new about three years ago. It's a gas fired furnace. I have a single story house. The furnace is in the basement, and the flue is ran through the old brick chimney, and out through the roof.

Due to brick chimney water leaks above the roof line, I had the brick chimney removed down to the underside of the roof. Then had the flue pipe flashed at the roof line, with the sheathing and shingles reworked to seal the new flue termination through the roof. Hope this makes sense.

What do you think ??
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Old 01-14-17, 05:53 AM
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Hi skooter, the pros will be along but I wanted to comment.

Burning gas produces a lot of water as a byproduct. To avoid condensation inside the chimney they will specify a smaller flue size to keep the exhaust moving fast enough to exit the top before it cools below the dew point where condensation will form. What size is the flue pipe and is it double wall construction, which would provide some protection from the cold.

I'll make a chimney watcher out of you. As you drive around (be careful) notice the moisture vapor exiting the chimney on other homes. If the vapor forma a clout above the chimney then it is warm enough to avoid condensation. If it has already formed a vapor cloud as it exits, it can be condensing inside the chimney. How far down that cloud is forming is unknown, but it raises the concern. My guess is your vapor cloud is is starting inside your chimney.

Size and type of flue??

Old 01-14-17, 06:30 AM
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The flue must be a above the top of the roof line. Can you post a pic?
Old 01-16-17, 01:29 PM
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Thanks for the info !! I'm pretty sure it's single wall running from the roof line to the cap. So that's part of my problem.

I'm going to have to wait a day or two to be able to post a picture, as we just got a half inch of ice. I'm in no shape to be trying to walk on that stuff at my age.

Give me a couple days for the picture. Going off memory, which isn't the best anymore either, LOL, i'm pretty sure the termination cap is above the roof line, but need to verify that.

To be continued......
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