Chimney repair for old unused flue

Question

We bought a house, built in 1986. The home has a "real" fireplace (heatilator style)- (Center flue), furnace is direct vented (now), and water heater is vented through the chimney (right flue).

The Chimney has three flues:

So here is my question....

Clearly water is getting into the chimney. It probably has been for years. I'm confused on why someone would break down a flue like this and leave it open to the elements? The house plans show the left hand side flue as being used originally for the furnace, so when they went direct vent, I "guess" they capped it off? But when you look at the water heater vent you can see it was once much larger, like for the furnace?

So I suppose it is possible this flue was never used? Clearly repair work has been performed up top to include mastic, and new caps. Why would no one cap off this flue?

I've called some masonry contractors in the area and am awaiting a visit from one of them. Should I consider using silicone/mastic and repairing the cracks and capping the flue flush to the crown with a piece of ceramic tile/stainless/aluminum OR should I consider a full chimney chase cover which I'm assuming could be cheaper in the long run as I would not have to have it resealed often or worry about more cracks in the crown?

Seeing the basement picture and the open flue picture, I'm under the impression the structure of the chimney is fine internally, am I being unrealistic given that this has been this way for a minimum of 5 years (winters, rain etc)?

Answer 1

I've had two masonry contractors out. They both agreed the flue is unused, both stated it is a dummy flue. I'm not convinced, but it doesn't matter.

Both noted the water getting inside. Booth discussed the cream of the crop solution, New crown. Neither oversold it.

One liked the idea of metal cap, one never heard of it, lol.

Both suggested to cementing cap the dummy flue and sealing cracks. As I know I'll never use this flue, it made enough sense, I went this approach.

Job done as it was the simplest most immediate solution. I suspect in the near future, maybe next season, I will do a stainless, or all out copper top, with a drip edge, as its astute top lady longer than concrete in wet snowy buffalo weather.