Fireplaces, Heating Stoves, Flues and Chimneys - funny smell?

Hi, indoor fireplace in living room. Is used all the time throughout the winter. Real woodburning. I have used it before this winter and now I have a question. I am in my basement now, which was finished a few months ago, right after last winter was over with, and I am noticing a strange smell. It is very strong, and it smells exactly like roasting marshmallows. The only thing I can think of is that it is coming from the place where I empty the ashes out. Its a section in the wall where the ashes fall and collect and I clean it out by opening a door and removing them. But what's funny is that I've never smelled this smell before. And it's only downstairs; when you walk upstairs everything smells normal. Could it be from the fireplace or something else? Any comments would be appreciated. Thanks

Lots of time when its real cold out side. Say you have glass doors on the fire place the cold air will fall down the flue and on down the ash dump you have there to the basement and come out some down there. Also any vent fan running and trying to get air from there? You say wood burning fireplace. Most of the time we find people over fire them and by doing so warp the damper in them that they dont close tight as the should. This well let air down in it.

All I can say here is could be

ED ;)

No, no vent fan or anything. How could cold air come in from the top when hot air is going up? How do you over fire a fireplace?