Return to the Heating & Air Conditioning Forum | Post a Follow-Up

Chimney condensation

Posted by barrychan (My Page) on
Mon, Jan 4, 10 at 11:01


I bought this new construction in 2007 at new york city and have been battling with lots of leaks since we moved in. Luckily most of the leaks are resolved by the builder who built it and those that can't be resolved are resolved with the awning solution (that solved my patio leak).

Just when I thought all the leaks have been resolved; my chimney started to leak around the flue pipe area in the basement. I have two water heaters and 1 furnace connected to the chimney. It is leaking around the where the flue pipe connects to the chimney. Pictures located at

It doesn't leak in the spring,summer,fall and would leak throughout the winter. It started leaking when there is no precipitation on the outside and as the temperature gets colder outdoors, the leak starts getting worse and will continue until the March time frame. Do you guys have any idea of what can be done to fix this?? The contractor caulked and check the flashing around the roof and added more weep holes in the chimney but that still did not resolve the problem and has been leaking for 3 winters. I am suspecting that newer efficient appliances makes it worse and I have a pretty tall chimney around 40 feet. Thanks for your help.

Follow-Up Postings:

RE: Chimney condensation

hi barry -

I'm a fairly recent diy'er so you'd have to take anything I say with a grain of salt. I got into maintaining my own heating system (oil) in the last few years.

I believe you can get a lot of condensation in your chimney if the flue gases aren't hot enough coming off your furnace. I know heater service guys check the gases with a thermometer they stick in an access hole in the vent pipe - I think before the damper on the furnace side. The condensation I believe is bad for the chimney and can cause deterioration.

I can be going off on a tangent here. Hope some real pro's come to your aid.

Good luck!

RE: Chimney condensation

You need to contact a good heating co. that can do a stack
sizing for you. You will probably need a flue liner put down
your chimney, and out into the basement and then have all your flues put into it. Your cement chimney is probably to large and also if it is a outdoor chimney it does not get hot enough to draft good. A new aluminium liner sized right will make it work right. later paulbm

RE: Chimney condensation

Thanks champipple and paulbmfor the inputs. I was away for two weeks. I had a contractor come in and another guy from a heating company this past weekend. The contractor wanted to put another wall up where the flu connects in an attempt to keep the flu where it exits the wall as close as to the outside temperature.

This other guy from a heating company said to he would like to use double wall flue since he thinks the condensation is occurring where the flue exits into the wall. Now I understand what they are attempting to do and it sounds right to me (since i really don't know that much) but which solution would work the best?

Another detail I would like to add is the furnace and two water heaters are enclosed inside of a 5' by 10' room. Thanks!

RE: Chimney condensation


I haven't gone with either solution. I asked around and someone told me they make a fan that would help blow the flue gases and maybe that would solve the problem. Do you guys know if I could buy such a fan at home depot? Another thing I did is I bought this foil insulation wrap to wrap around the flue pipes of the water heater and furnace. It seems to help but hasn't stopped the condensation.

any help is appreciated. Thanks.

RE: Chimney condensation

chimney liner is the way to go. What is the size of the actual inside diam. of the chimney. how many btu geoing into the chimey, wat is the chimney pade out of on the inside? take that info to a supply house. Talk to a person behind the desk. Then have him recomend someone to check it out.

RE: Chimney condensation

chimney liner is the cheapest and best way to go.As wisehvac said the current size of the chimney you are using is most likly to large. calculations are in order. doublewall bvent chimney will work a bit better due to the double wall but more exspensive.

RE: Chimney condensation

I am hoping that you figured out why your chimney was creating so much condensation and what you ended up doing about it? I have the EXACT same problem in Baltimore and would love your advice.
One HVAC person said I probably need a new chimney liner- the other thinks the flue is clogged and that should fix it? HELP!

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here