Furnace duct question

[Clarence Martin]

Went out and bought a jar of that furnace pipe duct cement, Followed directions and did EXACTLY AS THE INSTRUCTIONS SAID. Cement dried hard. and I went up to check the furnace.


Well, the stuff did NOT WORK!!! The pail I left under the duct where it was leaking before , was filled with water!!

What are my options ? Can I wrap it with duct tape that is rated High Temp ? Will that stop the leak ?
The furnace pipe runs from the furnace , then makes a 90 turn to another section of pipe that goes straight up to the roof. It is the bottom of the section that goes straight up through the roof that is leaking.

The instructions on the furnace cement say to not expose to heat for 24 hrs. Kind of hard to do in the Winter!!!

[Ken Fitzgerald]

Clarence,

You shouldn't have water in a furnace vent.

Is there any evidence that the water is running down the exterior of the vertical pipe?

It sounds like the leak could well be at where the vertical pipe exits through the roof.

[Clarence Martin]

No leaking down the sidewalls on the outside of the pipe. Just leaking around the edges on the bottom of the pipe. Now, when the furnace turns off, I do hear a pinging or dripping sound. Can't tell if the sound is coming from the pipe or the furnace.

[Clarence Martin]

One thing that I always wondered , was could that pipe be redirected out through the side wall, instead of going up through the roof ? I know that the Gas Boiler Heater in the basement is ducted out through the side wall of the basement, and have never had any ventilation problems . Could that work with a forced hot air gas furnace ?

One furnace man said yes, another furnace man said no.

[Wade Lippman]

Is this a follow up to an earlier post? If not, it is kinda hard to understand what the problem is without any information.

There could be water from condensation in the exhaust, but there shouldn't be much.

[Jim Becker]

One thing that I always wondered , was could that pipe be redirected out through the side wall, instead of going up through the roof ? I know that the Gas Boiler Heater in the basement is ducted out through the side wall of the basement, and have never had any ventilation problems . Could that work with a forced hot air gas furnace ?

One furnace man said yes, another furnace man said no.

There are a number of factors involved with flue ducting and how it can travel; generally, the manufacturer of the furnace/appliance provides those specifications. What that unfortunately means, is that the answer could be "yes" or "no" to sidewall venting depending on the specific furnace you have.

But back to the matter at hand, it's troubling that you have that much moisture. It could be condensation or water from another source. Is the flu properly capped up above the roof? Is there a seal where the flue exits the chimney to prevent cold air from pouring down around the flue and causing more condensation? (Gas furnaces produce water vapor which is why there needs to be a condensate drain) More troubling is that you have a flue that has a leak. If water is coming out of it, what else might be coming out of it and into your home?

[ray hampton]

can snow or rain get into the furnace vent

[Clarence Martin]

Had a contractor open up the bottom cap to drain the water in the pipe today and see what the inside of that pipe looks like. About a full Thermos amount of water was in that pipe when he took the bottom cap off.

More troubling , is that I could see straight up to the end and nothing is blocking the pipe, but there is condensation dripping straight down the whole pipe. I know that the heating ducts ( They are all in the attic, unfortunately.) were all wrapped and there is 14 inches of insulation blown in the attic. Now I am not certain if the Furnace flue pipe was wrapped.

Contractor thinks that if the pipe was not wrapped, wrapping it might stop the condensation problem.

[Myk Rian]

More troubling , is that I could see straight up to the end and nothing is blocking the pipe, but there is condensation dripping straight down the whole pipe.

Contractor thinks that if the pipe was not wrapped, wrapping it might stop the condensation problem.

Well, I think you found the problem.

[Ole Anderson]

My guess is that you are getting condensation because the old flue pipe is sized too large for a newer, higher efficiency (or possibly smaller) furnace. If so there isn't enough heat going up that big flue to heat the pipe and air in it to keep the water vapor in suspension, so it condenses out on the relatively cool flue, the water runs down the pipe and exits at the first joint it sees. If that is the problem, you need a flue liner to decrease the size of the flue to an appropriate size. Any good HVAC guy should have no trouble finding the problem and solving it. If on the other hand you are getting rain water (or snow) down the flue, you simply need to add a cap. Western New York, huh? Could be that six feet of snow...

[Jim Becker]

Ole may very well be correct here. If it's a newer unit and the original flue was used, there could be a mis-match. But even if not, how the flue is setup through the chimney is important relative to dealing with condensation. Additionally, if it's not sloped correctly and setup to deal with condensation down below, the water will collect where it shouldn't...it doesn't matter if a gas furnace uses metal or PVC exhaust...provisions for condensation are mandatory for the install because water is a byproduct of burning natural gas.