New house with third flue to nowhere?

[CGStoker]

I recently bought my first house .

I used this forum a lot as a lurker when I was house hunting to get an idea of what to look for with fireplaces, chimneys etc. It was very helpful.

This place has two gas fireplace inserts, one on each floor. They each have a separate liner through separate flues on the same chimney. The upstairs insert is a Vermont Castings LHEC20, which seems to work well after a thorough cleaning and inspection. I haven't looked at the downstairs one other than a quick function test during the home inspection.

I spent some time yesterday poking around the chimney, and I found something that I'm a little curious about. The fireplace is off centre on the hearth, but there's an ash cleanout door on the outside of the chimney on what would be the right side when viewed from inside the house. Looking up from the cleanout door is a piece of drywall that looks like it's sagging, but if I'm eyeballing the measurements right the insert is still further to the side.

Possibly related, at the chimney cap there are three terra cotta flues. One (the right-most) is sealed up. There are no other appliances that tie into this chimney. The gas fired furnace and hot water heater are exhausted through a class A chimney on the other side of the house.

Does anyone have an idea what the third flue might be from, and also why there might be drywall across the void?

 

[EatenByLimestone]

Does it go to the basement?

 

[spudman99]

I see in the photo that your neighbors house in the distance also has a 3rd flue and it looks like it is operational. You might knock on their door and ask them.

 

[Ashful]

I see in the photo that your neighbors house in the distance also has a 3rd flue and it looks like it is operational. You might knock on their door and ask them.

Good eye!

 

[Woody Stover]

Hmmm, I've got a spare flue that I'm not using (two, total in the chimney) but I've never investigated it very far. I doesn't appear to come out anywhere. I covered the top of the unused flue. It's an external masonry chimney and there's a clean-out door on the exterior but I don't know where that goes, either. If I put on a room addition that encloses what is now the exterior portion of the chimney, I was thinking I could tap into the second flue from the other side of the chimney if I wanted another stove in the new room..

 

[billb3]

Our last house had an extra flue, a gang of three and we were pretty sure the house originally had a gas cook stove with a heater in the kitchen that required a vent.

 

[bholler]

It is probably just a dummy flue to make the top of the chimney look balanced. I we see them all the time here and I hate them they add an unessecary point for a potential failure.

 

[CGStoker]

This sounds very likely like what's going on. I didn't see any evidence of a third flue anywhere other than a cavity in the chimney. I didn't realize that was a thing that was done. Thanks for your insight.

It is probably just a dummy flue to make the top of the chimney look balanced. I we see them all the time here and I hate them they add an unessecary point for a potential failure.