Your problem has likely nothing to do with downdrafts, placement or chimney heights. Plain and simple, Duraflame "logs" are not logs (hardwood). They are a manufactured product (recycled provessed sawdust) impregnated with wax and paraffin oil. In short, they emit a strong odor which nearly always leaves a home smelling like fast-light charcoal briquettes. The best way to eliminate this problem is to eliminate the Duraflame logs. Try a good, dry hardwood. 😊