water leaking from chimney

house built in 1939. Water is leaking inside the basement, right where the flue pipe enters the brick chimney. The pipe is type b metalvent double wall pipe coming from furnace to the chimney, and it appears to change over to the stainless steel flexible flue liner, from what I can see. I am assuming this goes all the way up to top of chimney. Due to roof pitch and frost, I can not get on top to inspect. there is a constant drip coming out of here, It was about 25 degrees outside. there are not water lines in the area. To much water to blame on rainfall. All I can figure is condensation. If it is condensation, what can they do about it? I recommended HVAC guy, but once again, I want to know what is going on here and what is causing it.
Thanks!

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Needs a sealed cap on the flue?

  1. Does the flue/liner have a rain cap?

  2. Is the chimney crown/cap watertight to the flue/liner system?

Those 2 are self evident to check for

  1. Does the steel liner go all the way to the top? If not and the lower temperature flue gases from a new, more efficient furnace/boiler enter into a now oversized cold outside-the-warm-envelope tile flue, there definitely will be condensation.

  2. An HVAC technician should check the temperature of the flue gases entering the chimney. Minimum flue gas entry temps have been developed by some agencies. A bit of furnace/boiler efficiency may have to sacrificed to have warmer flue gases going up the stainless flue to prevent the condensation.