When I use the fireplace in my home my basement fills with fumes. It's not
so bad that I can see smoke but the smokey smell is strong enough that
spending time in the (finished) basement is not enjoyable. My house was
renovated at some point before I owned it and a closet was built in the
basement that houses the furnace and water heater. This closet is directly
below the fireplace. There is a access panel behind the furnace to access a
ash box below the fireplace. In the fireplace is a hinged door in the floor
of the firebox for ashes.

I have tried to seal the panel behind the furnace with duck tape but the
odor didn't change.

Any ideas? Is the furnace drawing the fumes down somehow?

Any help would be appreciated.

Thanks