Fireplaces can have an open firebox or a cover with a door. Smoke exits through an opening inside the chimney called the flue. A flat piece of metal called a damper controls airflow through the flue.
Though traditional fireplaces create a cozy atmosphere, as much as 90% of the heat goes up the chimney. Covers can limit drafts and increase efficiency.
Get a professional fireplace and chimney inspection every year, before the heating season starts. To limit dangerous creosote buildup, burn dried (seasoned) wood. Well-dried wood burns hotter and cleaner, which helps prevent creosote.