The ash pit in a fireplace is a compartment that is used for collecting ashes. It is a cavity surrounded by concrete or cinder blocks and has a small metal door.
The ash from the fireplaces is swept to the ash pit through the metal door. Some ash pits are designed to hold years of ashes, while others only hold the ashes of a few fires. Ash pits are made from fire-resistant materials so that fire from the ashes does not reach flammable materials, such as wood. Most ash pits have clean-out doors near the chimney for removing the old ashes from the pit.