I was thumbing through the Department of Energy Blog and saw a great article written by Drew Bittner on Fireplaces.
I believe the article correctly called out the fireplace on its wasteful ways by saying it is a "a great big hole going to the outdoors". Absolutely Drew! I couldn't have said it better myself.
Just because a fireplace flue and damper is tucked out of sight doesn't mean it does not let heat out or let cold drafts in. Also, when you go to use the fireplace you are just accelerating the rate it is exhausting your interior air. I consider it my personal crusade to let homeowners know that fireplace use does not always mean you are supplementing your homes furnace heat! In many cases fireplace use simply wastes furnace heat and wastes the wood or gas you burn in the fireplace. - Jason