Heating, Air Conditioning, Fridge, HVAC/Flue


Water heater vent
Water heater vent  

I just bought a house. I noticed that water is dripping from the water heater flue pipe in a couple spots onto the basement floor. The pipe travels horizontal before going vertically through the roof. The home has a high efficiency furnace but I suspect the old furnace was venting through the water heater vent prior to the installation of a high efficiency furnace.

I would like to know what might be causing water to form in what should be a gas vapor pipe and who I should call to fix it? I've had a roofer out to confirm that the surrounding chimney stack has a rain cover. A picture of the vent is attached.


There are several things that can cause flue pipe to drip.  The dripping is condensation.  The flue pipe is getting cold enough to allow moisture to condense on it.  One of the byproducts of burning gas is moisture.  The pipe could also be getting cold enough that the outside moisture air is the source.  From the picture it might appear the flue to too large for the water heater.  That gives the flue gas time to cool down and condense rather then being pushed outside.  If there was a furnace on the same flue, then that could explain the over sized pipe.


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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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