Q: Do Firepalces suck heat out of the house? - GD
A: GD, The short answer is YES!
An open fireplace is only 5% efficient at generating heat. Furthermore, the US Department of Energy has found that a person using an open fireplace during cold weather will use 10% more fuel to heat their home. So it is certainly a loosing proposition to generate heat with an open fireplace. The heat loss is at its peak when the fire burns low like in the picture.
Some people have mentioned closing the damper when the fireplace is not in use. That is certainly a good idea but dampers are notoriously leaky and crusty due to cresote and constant heating and cooling warp and metal fatigue.
It always makes me laugh when a person suggests opening a window to help your fireplace. Who wants to do that in cold weather? It certainly increases the draw for your chimney, but it obviously lets in a significant amount of cold air. I live up north, so i'm not into doing that in the winter! - Jason