Fireplaces are objects most commonly found in the Basement/Cellar, but they will appear in later chapters as well (except for The Womb/Utero). Two fireplaces will usually be present in the Shop, and always in a Devil Room.
Touching the flame will do 1/2 heart damage to the player, even if they possess a flight upgrade. However, enemies would also receive considerable damage if they happen to touch the fire. Hoppers are the only exception: they will turn into F.Hoppers, which are immune to the fire.
Fireplaces can be extinguished by shooting tears at them. This can cause them to drop a single heart or coin variant (a half-heart, full heart, soul heart, eternal heart, penny, nickel, or dime).
In Wrath of the Lamb, there is a chance for a normal fireplace to be replaced with Hellfireplace. These burn with a more intense orange and can sometimes shoot slow-travelling projectiles directly at the player, which also deal 1/2 heart of damage. If the player is killed by these projectiles, it will appear on the death note that a Gaper killed them. They drop items at the same rate as regular fireplaces, but will spawn them in the diagonally opposite corner instead of the actual location. They may be a reference to the Old Man from The Legend of Zelda. He would make the fires next to him shoot projectiles at Link if attacked.