A gas fireplace comprising a housing adapted to be located in a building. There is a first conduit in the housing to act as an air inlet. In insert is received within the housing. A second conduit in the insert aligns with and is received by the first conduit. The invention permits the construction of a gas fireplace in two stages, a first stage in which the housing is built into the building and a second, subsequent to all building activity, in which the insert is received within the housing.