There is an art to these things. If you want to have a "comfort room" with the gas fireplace, you must isolate it from the rest of the house.
But if you want to use the fireplace to heat the whole house, you have to establish a circulation path. Basically, heat rises, so you want to free the flow of warm air to the upper chambers, and perhaps use the back stair, (if you have one), to let the cooler air descend to be warmed again.
All of this you should get from your "Introduction to Basic Physics" class.
We’re planning to get dual-zone heat and air next year, so next winter we should be able to control the heater from upstairs, instead of the room with the oven and the gas fire. Our builder wasn’t bad overall - no disasters unattributable to children in the last five years - but putting it there was stupid.
You mean the one for "servants???"
“Back stair” in my dreams. The fire heats the dining room, and that’s it.