A fireplace insert is a device that is inserted into an existing fireplace to improve its efficiency. It typically consists of a metal GRATE, which is the 5-letter solution to the crossword, and a firebox that is designed to contain and direct the heat of the fire. Fireplace inserts are used to reduce heat loss and increase the amount of heat produced by the fireplace. They can also be used to reduce smoke and other pollutants from entering the home.