# Range hood condensation problem



## maddog1 (Aug 21, 2012)

My range hood vent moves a lot of CFM. The discharge goes up thru the attic space & vents out the roof. The attic pipe leading to the roof vent is a 8 inch dia. standard sheet metal pipe. In cold weather, if I use the range hood, I will get condensation forming & dripping down on to the oven. 

I'm assuming this is due to the fact I've got a warm air discharge from the stove passing into a Cold attic vent pipe. If I wrap the attic vent pipe with a Water Heater Thermal jacket in the attic will that solve my problem? Thanks.


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## christoff (Feb 26, 2008)

maddog1 said:


> My range hood vent moves a lot of CFM. The discharge goes up thru the attic space & vents out the roof. The attic pipe leading to the roof vent is a 8 inch dia. standard sheet metal pipe. In cold weather, if I use the range hood, I will get condensation forming & dripping down on to the oven.
> 
> I'm assuming this is due to the fact I've got a warm air discharge from the stove passing into a Cold attic vent pipe. If I wrap the attic vent pipe with a Water Heater Thermal jacket in the attic will that solve my problem? Thanks.


Have you tried wrapping insulation around it?


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## CodeMatters (Aug 16, 2017)

Yes, insulating the pipe should help.


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## maddog1 (Aug 21, 2012)

christoff said:


> Have you tried wrapping insulation around it?


 
That's what I'm asking about.


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## christoff (Feb 26, 2008)

maddog1 said:


> That's what I'm asking about.


I guess what i am saying is wrap it with some good r value insulation and you won't have to spend money on electricity heating the pipe..
worth a try first??


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## jlhaslip (Dec 31, 2009)

Up here in the Frozen North, we typically don't run them through the roof for this very reason.
Usually, the duct is run sideways and out an exterior wall or out a gable end of the roof line.

Wrapping the pipe helps to a degree, but also setting a bit of "pitch" to the pipe so any condensation runs to the exterior makes a bigger difference. It also reduces "blow back" which reduces the likelihood of having minus degree winds entering the pipe and turning the kitchen into a freezer. 

Yes, I have seen the temperatures in a wall cabinet at near freezing. 

Solved by setting some pitch so the pipe went straight up about three feet then run downhill to exit at a gable end. The cold won't climb uphill and run back into the range hood. Sort of like a trap for cold air.


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## maddog1 (Aug 21, 2012)

jlhaslip said:


> Up here in the Frozen North, we typically don't run them through the roof for this very reason.
> Usually, the duct is run sideways and out an exterior wall or out a gable end of the roof line.
> 
> Wrapping the pipe helps to a degree, but also setting a bit of "pitch" to the pipe so any condensation runs to the exterior makes a bigger difference. It also reduces "blow back" which reduces the likelihood of having minus degree winds entering the pipe and turning the kitchen into a freezer.
> ...


In my situation, I cannot run vent pipe thru a exterior wall. The only available path is thru the roof. If I were to run it to an exterior wall, I would need a vent pipe running about twenty feet to the wall. This is an "Open" floor plan. I have almost no interior walls so everything is within the center of the house. And let me ad--I Love it- Having no walls. My contractor did not like it & my Architect had a challenge with it. My wife was not sure at the time we built it. Now I would need dynamite to get her to move out of it. :vs_laugh:


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## Bud9051 (Nov 11, 2015)

Your suggestion of adding a good layer of insulation should help. When the fan is turned on it needs to warm up the inside surface of that duct to be above the dew point. Something you might try is to turn the fan on before you fire up any burners. Then it is just warm household air without the massive amount of water generated by the combustion process. I assume you are burning gas and not electric.

You didn't how many cfm, just large, but big exhaust fans can require make up air, especially if other appliances are naturally drafted, water heater or heating. But that can be another thread if needed.

Try more insulation and preheating that exhaust path a bit.

Bud


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## MikeHel64 (Jan 7, 2018)

Yeah a good layer of insulation should help


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## ChuckF. (Aug 25, 2013)

For insulation I would buy a bag of the foil-backed fiberglass insulation such as used to wrap hvac ducts with. Buy some aluminum hvac tape as well to fasten it. Both those products are made to survive attic extremes.

Water heater kits that I have seen are white plastic backed insulation, I don't know how that would perform in an attic or it tape would stick to it for long without turning gummy.


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