We recently purchased a house with a fireplace with a gas log. However, when we run the fireplace we have noticed black marks on things like the coffeemaker and the can opener. There is also a lot of black stuff on the mantel over the fireplace. Is there a vent or something that we haven't opened?

I have gas logs.
We keep the chimney vent closed. We haven't had any black marks on any thing.
Off hand I would say that maybe the adjustment of the logs is off and needs adjusting.