Smoke in the basement...can't raise flue

[masemase]

Hi everyone.

We have a smokey basement from our oil furnace flue and our wood fireplace flue meeting at the exit point. Unfortunately, there is a cement cap above the two flues. We did have a mason build a wall between the two, but it hasn't eliminated the smoke. What is the next-best solution? Should I wall off the sides of one of them so that smoke only goes out (or air only comes in) from one side? This seems like it would reduce, but not eliminate the problem.
While the smell is annoying, is it dangerous?
Picture shows a side of the chimney with the brick wall dividing the two flues in the middle. I hope I am using the right terms.

 

[kborndale]

Do you have a CO2 detector in the basement?

 

[DAKSY]

Is your fireplace an open wood burning type?
Is there an outside combustion air vent?
If so, is it open to the outside?

 

[masemase]

Do you have a CO2 detector in the basement?

Yes. It has not ever gone off. CO, right? Not CO2?

 

[masemase]

Is your fireplace an open wood burning type?
Is there an outside combustion air vent?
If so, is it open to the outside?

Good questions, thanks.
1. Yes open wood fireplace.
2. No vents. The fireplace and chimney are in the center of the house. In my mind, a large PVC pipe running from an exterior wall could serve this function, but it would be difficult and ugly as hell unless it came up from the basement. See photo to get a sense of the room. There is a room behind the fireplace as well.

You didn't ask, but we have an ash chute, that is sealed at the clean out door, but is still drafty. Would it be possible to purposely connect that to the exterior through the basement to provide makeup air? Cracking open a window makes everywhere else in the house too cold.

 

[DAKSY]

I think trying to get combustion air thru the clean out in the basement would exacerbate the situation. You need OUTSIDE air…

 

[masemase]

I was saying to connect a vent from the outside through the basement to the bottom of the ash chute

 

[brenndatomu]

I've seen various people here deal with a chimney like that several different ways...pop the top off and have a mason make it so they are different heights...or I think I recall someone having a hole cut in the stone cap and put an extension on the top of that flue