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chimney condensing issue

We have an old 1920's house with a central brick chimney. We replaced the boiler 10 yes ago with a peerless series MI 05 stdg wpc gas natural draft boiler. There is also a 40 gallon gas hot water heater venting into the chimney. We have had condensation issues with bleeding of dark sticky liquid thru the chimney mortar at its upper 8 feet on the coldest winter days. We have reroofed and reflashed, and put a 6" stainless liner into the chimney connected to both boiler and hot water heater. There is still condensing on the coldest days. We have also waterproofed the exterior part of the chimney and have been told the mortar and bricks are fine. There is a rain cap on the stainless steel flue and also, an old clay flue JUST at the top several feet. The clay flue protrudes about 5 inches above the brick and the stainless steel liner is about 10" above the clay flue. There are no icicles on its exterior. My contractor thinks its possible the clay flue might be causing the issue? Anything we should look for? Help needed....


  • Jack
    Jack Member Posts: 1,047
    Tile liner is not the problem

    The original mason screwed the original owner by shorting him a complete tile lined chimney, but we can assume he is long gone. The problem is the flue gases are cooling and condensing. Install an insulated vent connector first and see if that helps. Then if needed insulate the SS liner. Is there a block off plate at the top of the liner to prevent cold air from running down the chimney. I bet this could have been done with 5" too.
  • susan_shawn
    susan_shawn Member Posts: 2
    Where does the vent connector go?

    I am so GRATEFUL for your post. We are so baffled and frustrated by this problem.

    Where would the insulated vent connector be installed?

    Yes, the chimney does have a plate to prevent cold air from coming in. Should the plate be insulated?

    When you say this could have been done with 5", I assume you mean we could have put in a 5" stainless steel liner vs. a 6"...

    Could we box in the chimney outside where it protrudes from the roof and insulate it on its exterior? Would that help?
  • Ironman
    Ironman Member Posts: 7,399

    The flue connector is the part that connects the appliance to the liner. Insulating any part of the liner, particularly near the top, will help keep it hotter and reduce the chances of flue gases condensing.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.