i had a smokey fireplace, so i have been through all this....i forget what its called, rumsfield, rumsford...something like that. rumsford rule(if thats it) the chimney area needs to be 10% of the fireplace opening. i think thats what it is, so if you have a round chimney is PI(R)squared...i think. now...just like mentioned above if you play with the cardboard to close off some of the opening, and that works, you can actually get a nice peice of metal made up to cure it. also make sure your chimney is clean. then, check to make sure your chimney is high enough. chimney needs to be 2' higher than anything within 10'. make sure your chimney cap isnt too restrictive. when i bought my cabin something must have hit the chimney cap and smashed it down onto the pipe. i could have smoked meat in the house with my first fire. now, all that being said, glass doors should help as well. kind of depends what you looking to do with your fireplace. i think the draft on my fireplace is marginal at best, which to me means i am not sending too much excess heated air up the chimney. if i dont have a nice hot fire going, and the doors are open, i will get somke out. i also custom fabbed a blower grate into it, to blow heated air back into the room. and it does work to heat my house. efficiency is probably pretty low, cause fireplaces tend to gobble wood. but when everyone is there, they always like to have a fire going anyways.