Wood fuel is proven beyond any reasonable doubt to be carbon neutral. Unlike the common belief amongst peers, wood burning doesn't increase atmospheric carbon dioxide levels. Though wood logs will obviously emit carbon dioxide while burning, the carbon discharged will be counterbalanced by the growing trees. This is a fact since trees absorb carbon dioxide and emit pure oxygen which aids minimize the levels of carbon dioxide released into the atmosphere.
Many furnaces are also equipped with glass doors that are especially necessary when the fireplace is warming up and can not deal with smoke and thus lets the bitter smell in the room. The glass cover helps to prevent it. The doors can be swinging or lifting. By the way, furnaces with a fireproof door are safer than open grates, and allow you to manage the flow of warm air much better and easier. The only drawback is that sometimes the heat-proof glass may be covered with soot.