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.
It does not utilize wood so they are against the environment. Use of an electric fireplace doesn't produce any pollutant or harmful chemicals. There is no release of smoke from this kind of fireplace so there is no need for a chimney or venting system.