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Old 05-12-2012, 10:51 AM   #1
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Water leak through vertical flue


80% propane furnace w/6" double wall flue apparently leaked small amount of water this winter. Small area of discoloration where flue goes through sheet rock ceiling and dark water drop stains on top of furnace where flue attaches. No sign of the water being on the outside of the duct between sheet rock and furnace.

I am confused because it seems water is inside the flue (water gets carried to furnace on a 2' horizontal run) and on the outside of the flue as evidenced by water stains in ceiling sheetrock around flue penetration.

Maybe its from horizontal rain/snow and a different cap would be required. Lots of wind here.

House is 1 year old. Shingles around roof jack look perfect. Sealant at seam between roof jack and flue could be better.

What sealant would be good for roof jack to flue seam?

Could moisture just be from condensate? Pretty cold winters here in northern Nevada at 6000'.
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Old 05-12-2012, 11:39 AM   #2
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Water leak through vertical flue


What size is the furnace.
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Old 05-12-2012, 11:50 AM   #3
how
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Water leak through vertical flue


Are you talking about condensation?
Warm moisture laden house air condensing (in the attic) on the exterior side of the vertical vent that then stains your gyproc ceiling?
Warm moisture laden furnace combustion gases that are condensing inside the vent as they cool on their way out? These will appear at vent joints, the "B" to "C" vent transition and the top of the furnace.
Poor roof seals where the vent exits?
The need for a wider vent cap to stop wind blown rain from entering?

All are common issues in my area. Condensation problems are usually issues around incorrect vent sizing for the full BTU usage, venting through un insulated spaces, vents with long incorrectly sloped horizontal sections, homes that are consistantly allowed to get too cold, etc.

Last edited by how; 05-12-2012 at 12:08 PM.
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Old 05-13-2012, 12:13 PM   #4
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Water leak through vertical flue


Quote:
Originally Posted by how View Post
Are you talking about condensation?
Warm moisture laden house air condensing (in the attic) on the exterior side of the vertical vent that then stains your gyproc ceiling?
Warm moisture laden furnace combustion gases that are condensing inside the vent as they cool on their way out? These will appear at vent joints, the "B" to "C" vent transition and the top of the furnace.
Poor roof seals where the vent exits?
The need for a wider vent cap to stop wind blown rain from entering?

All are common issues in my area. Condensation problems are usually issues around incorrect vent sizing for the full BTU usage, venting through un insulated spaces, vents with long incorrectly sloped horizontal sections, homes that are consistantly allowed to get too cold, etc.
Furnace size is 108,000.


The leak looks so small that I thought condensate or condesation of flue gases could be the culprit.
Heres a better description of installation: Furnace and water heater are in insulated garage on raised platform. Garage is heated to 60 most days with seperate electric heater. 4" single wall flue leaves furnace at 45 degrees for 3' then attaches to "Y" at bottom of vertical 6" double wall that penetrates sheetrock into well insulated attic for 4' then through roof and extends 2' above shingles where it terminates with a 10" round cap with grill like openings on its periphery. 3" flue from water heater attaches to other leg of "Y" inside garage. Attic is shared by entire 2200 sq ft single level home and is well insulated. House is at 60 degrees 16 hrs/day then raised to 70. All joints are metal taped.
Installation passed local inspection and looks well done but more to learn about that.

So I guess its a process of elimination starting with sealing the roof jack then changing caps if that doesn't work. Can you suggest and exterior sealant for jack to flue seam?
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