This is a relatively common problem & there can be many causing factors to consider. 1) Has your chimney been swept lately? If not, your problem could be caused by a build up of soot, tar or another blockage, perhaps a birds nest in your chimney. This may restrict the draw in your flue as the smoke has nowhere else to go but back down into the room. 2) Is your chimney the correct size for your appliance?  If your flue is…