Condensation on exhaust pipe

Old 01-03-10, 08:57 AM
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Condensation on exhaust pipe

I have a 3.5 inch PVC exhaust pipe for my high efficiency gas furnace. The exhaust pipe travels up from the furnace on the first floor through a closet on the second floor and exits to the outside from the closet. When the outdoor temperature is cold and windy like today (22 degrees & windy), the PVC exhaust pipe gets cold and condensation develops on the pipe. Is there a way to prevent the condensation, would insulation help? If I insulate the pipe, is there a specific type that I should use?
Old 01-03-10, 09:37 AM
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Do you hang clothes in those closets? I would seriously think about re-routing that thing outside the house.
Old 01-03-10, 11:18 AM
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Condensation on the exhaust vent pipe is normal and expected. It's why they call these high efficiency furnaces condensing gas furnaces!

Natural gas has a lot of hydrogen in it, and when the gas burns it produces water vapor from the hydrogen and oxygen. Just as it takes a lot of energy to convert water into steam, if you condense steam into water you gain a similar amount of energy back, plus you get to extract more heat by cooling the combustion gasses down to 120' F. or so.

That liquid condensate should flow back to the furnace where it is pumped out or flows outdoors or to a drain by gravity.

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