Water dripping down furnace flue vent

[rationull]

Occasionally when it rains I'll get some water dripping down through my furnace's flue. Not flowing or anything, but drips that come out at the top of the furnace where the vent is attached and run down the furnace and onto the platform it's sitting on. It seems like this only happens when it rains hard for several hours or more. I just end up putting some towels at the bottom to absorb the moisture and try to turn the thing up high enough that it runs regularly to evaporate all the water.

The furnace is 20 years old. Is this normal at all? I realize it's not "normal" for a new installation (or at least, better not be) but is it common on older ones? I haven't gotten on the roof to check the vent cover yet but it's on there, and I think if it were really bad I'd be seeing more water. Since it's coming down through the pipe I don't think it's a sealing issue around the vent.

I'm just trying to figure out how much I need to worry about this. The whole furnace is going to need some TLC but I'm trying to wait until late spring or summer to deal with it so I don't run the risk of ruining something and being without heat.

 

[Pop_Rivit]

It's time to get up on the roof and figure out why water is coming in. It's probably a bad cap or some of the flashing/sealant around pipe has dried up and cracked. If it were mine I'd fix it now.

 

[Ausfahrt]

Originally Posted By: Pop_Rivit
It's time to get up on the roof and figure out why water is coming in. It's probably a bad cap or some of the flashing/sealant around pipe has dried up and cracked. If it were mine I'd fix it now.


+1

The water you see may only be a small fraction of the water that is leaking through your roof. You need to check it out ASAP.

 

[duaneb9729]

normally there is a "Tee" installed that has a drip leg that helps the water pool and evaporate.

It sounds like its condensation on the inside of the flu piping.

Could you post a picture?

 

[rationull]

I'm not really sure what I would post a picture of exactly. I don't think it's leaking through the roof; if it were it seems like the water would be dripping down along the outside of the flue pipe but it's definitely on the inside.

I don't think it's condensation since it happens when the heater is off.

I will get up there and check it out as soon as it's not raining on a weekend.

 

[Pop_Rivit]

Originally Posted By: rationull
I'm not really sure what I would post a picture of exactly. I don't think it's leaking through the roof; if it were it seems like the water would be dripping down along the outside of the flue pipe but it's definitely on the inside.

I don't think it's condensation since it happens when the heater is off.

I will get up there and check it out as soon as it's not raining on a weekend.


Since it happens only during times of heavy rain I suspect the chimney cap may be rusted or blown off/askew.

It is possible that the heat exchanger is causing the issue-a cracked heat exchanger can cause condensation on the pipe. But since it only happens during storms I'm still leaning toward either rainwater penetrating the cap or the increase in humidity from the rain causing condensation. I'd be concerned-the water could eventually cause the pipes to rust if it's not corrected, not to mention that the water dripping onto the furnace doesn't do it any good.

You do have a CO detector in the house-right?

 

[duaneb9729]

a picture of the lower part of your chimney before it heads up though the house would help me help you. This is my profession and rather than operate from assumptions or forgetting to ask one more question, a picture can answer many questions at once.

My guess is that you dont have a tee installed and the condensation or rain runs down the pipes toward the furnace and the water heater. The tee protects those items from rusting excessively.

 

[rationull]

I've got a CO detector in the room with the furnace and another next to a furnace vent in the bedroom.

The water isn't actually dripping anywhere on the furnace where it's going to do any harm, it just runs down the face of it. Not to say I shouldn't fix the problem of course.

duane: If there's supposed to be a tee visible before the pipe disappears into the ceiling then I'm pretty sure there's not one installed. I will try to get a picture of that area tonight and post it.

 

[rationull]

Here's the setup:

The water drips out at the top of the furnace and runs down the front.

 

[mechtech2]

Hard rain can blow sideways and get into a vent and run down.
I'm pretty sure this is what is happening.

I have a free standing fireplace that does this several times a year.
I also use the towel technique.


But I know for sure what is happening. At this point, you do not. So check it out.

 

[doitmyself]

That looks like double wall vent. Does that serve as your chimney also, or does that go into another type chimney, ie., masonary?

You could have some kind of compromise (joints/seams) in the outer wall of the double wall pipe.

So, repeating others advice, above the roof you need to look at the roof flashing joint, the chimney (double wall) joints/seams, and finally the chimney cap and its connection. At any place there may be an avenue for a tiny stream of water to be getting inside the double wall.

 

[rationull]

I have thought of the "sideways rain" possibility and that does seem like the most likely scenario since it doesn't seem to happen with lighter rain.

The vent is only double walled until that last curve piece connecting to the furnace. If it were a compromise in the outer wall I would think the drips would come out where the last double walled section ends, right?

Originally Posted By: doitmyself
That looks like double wall vent. Does that serve as your chimney also, or does that go into another type chimney, ie., masonary?


It's just the exhaust gas flue for the furnace and the water heater.

 

[labman]

Spring is coming. When you can do without the furnace, block off the chimney and see if water comes in.

 

[Samilcar]

Originally Posted By: mechtech2
Hard rain can blow sideways and get into a vent and run down.
I'm pretty sure this is what is happening.



This happens with my gas water heater flue pipe. If it rains hard AND there is a lot of wind, the rain blows sideways into the flue cap and down the inside of the pipe into our basement.