Smoke coming down second flue

We lit a fire for the holiday, sounds crazy right? There is three flues in this chimney. One that isn't used that was for the old oil boiler and the other two are for fireplaces. One on the first floor and a second one in the basement. The draft is controlled with a spring loaded cap on the top of flue. the chain comes all the way down the flue liner. All three pipes have SS liners, how far they extend with the fireplaces I'm not sure. I checked them in the fall and they looked clean as a whistle, I'm not eve sure if they were used after they were originally installed and we have barely used them.

So here's the thing, I lit a fire in the first floor fireplace and I noticed some smoke in the basement. It was coming down the chimney for the other fireplace. My first thought was the cap wasn't sealed tight on the top of the flue it was makeup air pulling smoke down it. However when I opened it no more smoke. My only conclusion is the smoke in the flue for the first floor is making it's way into the other flue and since it's capped on the top it's coming down. Sound right?

I've had this happen. Three flue chimneys reversing draft

It's only reversed if the cap is closed though. That's what is making no sense. As I said the only conclusion I can draw is somewhere in the middle it's crossing over to the other flue and since it has no where to go with it capped it's going down.

might pay to get a camera run down thru them see wats happening...

Richard,
Do the chimneys share a common cleanout at the bottom?

I had this condition with a chimney. Two flues terminating next to each other. I stuffed a rag in the opening of the second flue in the basement. That stopped it. Caused by a down draft in the second flue.

Richard S. wrote:It's only reversed if the cap is closed though. That's what is making no sense.

That is weird.

Was it just a whiff of smoke or lots?
When you opened the cap on the downstairs fireplace it might have let the chimney start drafting on it's own but when it was closed it might have had a slight downdraft going because it was cool pulling some smoke down...?
Does it start smoking again when you close it again?
Is smoke only coming out the correct flue at the top or can you see smoke coming out of the one for basement fireplace too?
Are these chimneys on an exterior wall of the house?

Sorry for all the questions

waldo lemieux wrote:Richard,
Do the chimneys share a common cleanout at the bottom?

No and there is only two cleanouts. The basement fireplace has none for obvious reasons.

coalkirk wrote:I stuffed a rag in the opening of the second flue in the basement. That stopped it. Caused by a down draft in the second flue.

There is complete cap on the top of flue, it's spring loaded...

That's not the point though, the smoke is only coming in when the cap is closed.

rockwood wrote:Was it just a whiff of smoke or lots?

I would have been lot if I didn't notice it.

Does it start smoking again when you close it again?

Yes but I only did that once.

Is smoke only coming out the correct flue at the top or can you see smoke coming out of the one for basement fireplace too?

Unless I get on the roof it's impossible to understand exactly where it's coming from.

Are these chimneys on an exterior wall of the house?

Interior.

This is a weird one...I'd be curious to know what you figure out with it

rockwood wrote:This is a weird one...I'd be curious to know what you figure out with it

We wont be lighting it again until next Christmas unless there is some kind of extraordinary event like the eletrci is out for a few weeks and I can't get fuel for the generator. I'll wait until the spring to look into it further.

Richard S. wrote:I would have been lot if I didn't notice it.

Just to add this was a steady stream of smoke, it was slow moving. It was certainly enough you could see the air was a little hazy and that was after about 1/2 of burning. That dissipated pretty quick once I stopped it from coming in.

Hi Richard,is it possible that the refractory cement between the flue liners is missing and the smoke is building up and getting sucked into the other flue with the cap closed but when you open it up it just goes out the top .I remember 23 years ago when I put in my new wood stove and SS liner I sealed up the top plate that the liner sat on with silicone sealer and when I lit the stove the oil on the liner started to burn off I was getting smoke in the house through the cracks in the clay liners and the mortar joints in the chimney,I removed the sealer and the smoke stopped coming into the house,just a thought.Keepaeyeonit