Smoke connects between two fires - GIF

[bruce.desertrat]

Ahhh, Light dawns! Thanks!

[old kodger]

no, creating one

[Haroun]

Likely there's communication from one flue to the other. I used to lead a meditation group in a building with fireplaces on the 1st & 2nd floors, they shared the same chimney , separate flues next to each other at the top. Even cracking a window upstairs when I would light the fire in the upstairs fireplace wasn't enough to stop the draw of air down the 1st floor chimney, cycling smoke through the building. You could watch the smoke rise up out of the one flue & head down the other. Lighting a candle & placing it in the 1st floor fireplace as soon as I entered would heat the air in the flue & start a draft sufficient to keep the cycle from starting.