I have a few known air leaks, most rather small, around a couple doors. They really are minor and I figured it was beter than too tight a house. Recently I noticed a sizable leak of cold air escaping past my prefab fireplace. I feel this comes from cold air collapsing down my chimney chase. My question is about the air volume balance that mustbe going on in my house. I assume the volume of cold air leaking in means I have other air escaping (else my house would be airtight and no inbound leakage). it probably is warmer somehow leaking out upstairs although I don't know of any specific locations. The only places I can think of are my two bathroom fans - but wouldn't they have baffles that open/close when the fan is turned on? Or are these fans simply large sources of air escaping my house?