DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   HVAC (
-   -   Furnace exhaust stack related leak (

Michael Ku 12-09-2011 04:29 PM

Furnace exhaust stack related leak
2 Attachment(s)

I have been unsuccessful in my information search regarding my issue, so I joined up and decided to post my problem.

For the last couple of years I have been dealing with a furnace-related basement leak. The furnace is approximately 10 years old. It vents through the basement wall and then up the chimney. A 4" double-walled venting pipe runs through the 4th cement brick down the basement wall. The leak drips out between the outer and inner walls of the vent pipe - through a 1/8" gap. It drips fairly continuously all winter and not at all in the summer. Thus, it appears to be a ground water leak, since winter is when the ground is saturated with water.

I dug down about two cement blocks on the exterior chimney wall this summer and found a few cracks. I filled them hoping to have sorted the matter out. Unfortunely, with the return of the wet ground came the return of the leak. I can only imagine that I did not dig down far enough. I am posting this message in order to see if anyone else has had a similar experience or might have some ideas that I have failed to consider. I am tempted simply to seal the offending gap with silicone. I fear, however, that the water may then find its way into the inner pipe and run into the furnace, which is down hill of the leak.



COLDIRON 12-09-2011 04:41 PM

If it only happens in the Winter it means your flue exhaust is condensing and dripping water back through it. Somethings wrong with the chimney or the pipe sizing, or the drafting. Might need a PRO or wait for other replies from other people for ideas.

ben's plumbing 12-09-2011 04:42 PM

if you could get some pictures would help....I think your problem is going to be condensation from chimney.

Michael Ku 12-09-2011 05:44 PM

Thanks guys for your input. I added a couple of photos to the original post.

ben's plumbing 12-09-2011 07:20 PM

is there a flue linner in the chimney ? thats a flexable pipe comming out of top of chimney... looks like you have single wall pipe from furnace to chimney...It really should be b vent double wall pipe....

Michael Ku 12-09-2011 07:42 PM

Flex-Liner Kit: Part # AFL
Yes, it appears to have a chimney liner, at least going into the wall (Flexi-Liner Part # AFL). Checking the top of the chimney will have to wait until the snow melts and I can safely get on the roof. I like condensation theory. It seems promising, 'though I admit that I don't fully understand it.

ben's plumbing 12-09-2011 08:01 PM

if there is a linner then iwould try b vent from furnace to linner.would keep flue gases hotter and heat up linner faster.....

ben's plumbing 12-09-2011 08:12 PM

you don;t have to get on roof to see if there is a linner...just look to see if a pipe is setting on top of chimney......

Michael Ku 12-09-2011 08:12 PM

I greatly appreciate the advice. I'm new to b-venting - that is, I don't even know what it means. I'm pretty handy, however, and will do some independent research. If you could possibly provide a bit more detail that would help me with google-searching for a more complete explanation. I understand the principle of sending some of the hot gases into the liner to heat it up quicker - great idea. I'm stuck on the how to do that safely part.

I will have a look at the top of the chimney in the morning.

ben's plumbing 12-09-2011 08:20 PM

most of the local stores handle b vent pipe and big deal need to measure lengths of pipe you need .....thats the only draw back can't cut to fit b vent ...looks like you need 2-4"b-vent 90 degree ells 1-30 or36" pipe and 1-48" pipe....these are just a guess looking at pipcs...

Michael Ku 12-09-2011 08:25 PM

Oh, I see, I am going to run a new pipe from the furnace to the wall, using b-vent pipe, correct? (whatever that is, I still have to look it up)

ben's plumbing 12-09-2011 08:30 PM

yes you got it i listed what I think you need just ask for those items in b-vent ...or double wall pipe...

Michael Ku 12-09-2011 08:40 PM

Gee, thanks! I may not get to it right away. But I will update this post when I do.

ben's plumbing 12-09-2011 08:42 PM

good deal ben

Michael Ku 12-10-2011 07:27 PM

O.K., this the part where you contribute your findings to help out some other fellow, right? :)

When I moved in to this house about three years ago it had a simple mercury thermostat on the wall. So to save money I went out and purchased a programmable thermostat. As you now know, I don't know very much about furnaces. So I hooked up the new thermostat and figured "Bob's you're uncle." - wrong

After sorting out with Ben that the problem was probably condensation and not ground water inflitration (I feel pretty dumb about that one) I did some research on the matter and discovered that things can get complex pretty fast. I read a post about a fellow who replaced the pipe from the furnace to the wall with b-vent pipe, but it did not completely sort the matter out. I also read an article on short-cycling of the furnace. It seemed to me that my furnace was short-cycling. So I dug up the manual for the thermostat. Now, I will refrain from swearing here, but the default setting specifies 5 cycles per hour! Fortunately, you can disable it. Now the furnace simply come on with a fixed span of + or -1 degree F. Guess what, the dripping stopped! Unless something changes, I appear to have entirely sorted the matter out by having my programmable thermostat behave like a mercury thermostat.:thumbsup:

Why would they have a furnace cycle 5 times an hour? Is that for 92+ effecient furnaces? Mine is your garden variety 80 machine - oh well.

All times are GMT -5. The time now is 07:43 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1