I have a house that is over 60 years old. There are fireplaces on the first floor and just below it in the basement. They appear to share the same chimney. I assume there are separate pipes going up the chimney but do not know. When we build a fire in the first floor fireplace, the basement smells like smoke. Why? THe first floor is not smokey, so I assume it is drawing okay. Am I wrong? ANy thoughts?