Hi Julie, that is the chimney - there are no ventilation grilles. The mantel is the wood piece across the front. I think there is a double walled metal chimney inside above the firebox that lets in make up air. The heat radiates through the glass - there might be a vent in the front just above the glass, I can't remember for sure. It is a prefab gas fireplace, most likely by Superior or Majestic.

Ok thank you so much for your time !