Water getting in flue

Old 11-10-16, 02:27 PM
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Water getting in flue

I have a gas furnace in my 4 story townhouse. Flue is on the roof, furnace on the 1st floor. I am getting a small amount of water in the flue. It is not every time it rains (I think). I can hear it drip though and hit the top of my ventless fireplace (flue runs near fireplace).

At first I thought it could be coming in the top. I put a bag over it one time when I was getting water and it didn't stop it.

Now I think it is where the 2 pieces connect about 8 inches above the roofline. My question is, what do I use to seal this better? The roof itself is a rubber membrane with a silver coating.

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Old 11-10-16, 02:33 PM
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Are you sure it's rain water and not condensation?
Old 11-10-16, 03:08 PM
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Pretty sure. It only happens when it rains. It happens even when the furnace is not being used (like summer).

Besides hearing it hit the metal top of the fireplace (when doing some construction I noticed some staining in the fireplace cavity), inside the furnace there are signs of rust. My guess is though since the flue is 30+ feet long most of the water is seeping out at seems at turns in the metal.
Old 11-10-16, 03:58 PM
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The manufacturer of the vent and perhaps the model number of the vent material ought to be stamped or listed on it.

I'd look that up and read the manufacturer's instructions for installing the vent.

Just looking at it, I wonder if the shield just above the wood deck belongs down right at the surface of the roofing. That's one thing I'd check.

Also, in general vent pipe should extend two feet above any point within a radius of ten feet from where the vent terminates. Your vent look several feet too low. That might cause venting problems.

If you can't find the name and model of the vent pipe, you could look at any or several manufacturers of such class B vent, such as Metalbestos and see what they recommend for installation.

It looks like you have easy access to your vent! Lucky, lucky!
Old 11-11-16, 12:00 AM
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I would also check the connection below the deck to ensure it is sealed properly with a rain collar as well. The rain collar above the deck is probably not doing anything positive to keep water away from that connection. The wood is too close to the pipe as well, as I believe you need a 2" clearance from any combustible material.

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