? water appearing on stones around fireplace ?

[djbartu]

I have a chimney that houses the flues for both the fireplace and the furnace. The inside is finished off with stonework up to the ceiling. Water has been appearing near the ceiling on the left side where the furnace flue is. I cannot figure out where the water is coming from. I've checked outside on the roof; there is no snow piled up, no apparant holes or damage to the shingles (installed about 3 years ago) and all of the step flashing appears to have been done correctly (I've even added some extra silicone caulking to ensure a good seal.) Where can this water be coming from? Is it possible that moisture in the exhaust from the oil furnace is seeping through to the inside? The stones seem to be wet all of the time, even though we may not have had any snow or rain for days. It has been very cold here in Northeast PA so the furnace has been running a lot. Let me know if you have any ideas. Thanks, Denis

[Troy]

Now I live in the south, so I don't know how good my advice is, but I think the exhaust from the oil furnace is a good guess.

Do you mean the moisture exists, even days after any precipitation? If so, I would think we could eliminate that as a cause.

Any other ideas?

[metalhd2]

Denis,

It sounds like the problem is condensation caused by the
temperature difference inside the oil furnace flue to the
outside of stones on the chimney. One solution is to install
a flue liner from the furnace vent to termination. My company
has done this in older houses with dual flues. It is not in-
expensive so I would get several HVAC contractors to estimate
the job.