While gas is used for a battery backup solution, in the penthouse, it is also for the fireplace. The chimney will be integrated into the building to hopefully hide it from sight. One idea is a chimney pipe that will go out the side of the exterior wall, and expel the fumes that way. I am not an expert in this area, so I won’t know if something like that will work, but this would be my hope. Even if not, an unsightly chimney will have to do. The gas fireplace is intended for comfort of heat, or when a mood needs to be set. With underfloor radiant heating, there is no actual need for a fireplace. With that said, it is a convenience and a want feature more than anything. I do know of electric fireplaces, but I would be concerned that the fire will look fake, and waste the cost of the electric fireplace.