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Question DetailsAsked on 4/20/2015

Have water leaking on my stove from overhead exhaust fan but it has not been raining

just started two days ago and only the exhaust tube is wet not wall .

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1 Answer


Assuming this is an exhaust duct that goes vertically up - not out through the wall, in which caseonly case 1) or case 3) from eaveice damming would likely apply.

Pretty late in the season for this, but three common causes - aside from the obvious leakage from a water pipe or air conditioner in the attic.

1) frost built up in the ducting due to prolonged (several days) without the over-stove exhaust fan being used in very cold weather, so the moisture from cooking and household air, which is continually going up the exhaust duct at low flow rate, condenses and freezes in the duct, then when the fan is turned on or the outside air warms up so the attic gets above freezing, it melts and runs down the duct and comes out at the fan. generally requires outside air temps below about 10 for the attic ducting to get cold enough to do that. Commonly if you remove the grease filter you can see up into the duct with a strong flashlight and mirror and see the frost buildup in the ducting.

2) similar situation, but frost buildup in the attic from air leakage up from the house (or exhaust vents vented into the attic instead of through the roof) cause frosting on the framing and sheathing, which then melts as the weather gets warmer and runs down through the insulation to the vapor barrier, and leaks into the living spaces around penetrations like exhaust ducts. In extreme cases this frost buildup can reach feet in thickness.

3) ice glaciering or ice damming on the roof or in the bottom of the snowpack (either from rainfall on snow, ice damming, or daily melting of the snow and icing at the exposed bottom edge at night damming up the water in the snowpack), resulting in water getting through the roofing and sheathing and dripping down inside the attic, or backing up around the exhaust vent/duct penetration and leaking in there.

Either way, you need to locate the source - go in attic to look for frost and wetness on the underside of the roof and on the framing and possibly also builtup on top of the insulation. If the problem is frost within the exhaust ducting, it may run down inside the duct, or leak through joints and run down the outside of it, depending on which way the ducting was installed.

If you are unable to inspect this yourself and don't have a friend who can check the attic, I would recommend a Roofer as the most versatile contractor type to locate and stop it -mostly because he is not going to be afraid or reluctant to get on the roof if necessary.

Answered 4 years ago by LCD

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