A flame simulating assembly having a housing including a top panel, two or more side panels supporting the top panel, a back panel connecting the side panels, and one or more front panels positioned substantially opposite to the back panel. Also, the assembly has a simulated fuel bed, a screen positioned behind the simulated fuel bed, and a flame image subassembly for providing images of flames on the screen, and the screen, the housing and the simulated fuel bed define an internal chamber. The assembly also has a fan positioned to provide an air flow through the chamber from one or more intake apertures to one or more exit apertures, through which said air exits the chamber, and one or more filters for filtering at least a portion of said air in the air flow. The internal chamber is substantially airtight, except for the intake and exit apertures.