Right.
As the fire dies down the updraft that was created by the heat generated lessens and then air is allowed back in to equalize the pressue differential.
Beginning the fire and almost out the same conditions can be present.
I have seen this happen and also have reproduced and demonstrated it.
Also other sources such as furnaces, stove exhaust draft hoods, attic fans, air conditioning, additional fireplaces in use, and openings away from the wind loaded side of the house (leeching) can pull air down that, or any flue.
What would I know?![]()
REX
Rex thanks for the imput, I think allowing the logs/fire to cool down as much as I did was 90% of it. We usually burn Pine which burns pretty Hot, not sure what was in there this last time though.