The distinction between a log set and an insert lies in their design and installation:
Log Set: A log set consists of a burner that generates flames and ceramic fiber or refractory concrete logs arranged on top of the burner. It is designed to be placed inside a pre-fabricated firebox or a wood-burning brick fireplace.
Insert: Both pre-fabricated fireplaces and wood-burning brick fireplaces can be upgraded with an insert. An insert is a fully contained unit enclosed in a sealed metal box with a glass front. It can either be integrated during the home’s construction or retrofitted into an existing wood-burning fireplace.