Accessories - Housewares - Finishing Touches - Need Help..Ideas [for closing off opening]

I am looking for help/ideas. In my Town home, my family room has a 20' ceiling with a ceiling fan that I installed. My living room is on the same wall, with an opening of 100 inches (height) x 41 inches (length). I am open to ideas to put something there to help keep the heat from escaping the living room. I don’t know what to put up. Whether it is temporary or permanent. Can anyone make a suggestion to help?

i'm not sure i understand. you want to close off the LR from the FR? and why do you want to block the air circulation? is one of the rooms unused?

there's just a 3.5 x 8 doorway in between them? i think the best looking solution would be a single french door (divided light door).

Thanks for your input. However, the part I would like to close off for the winter is not a door way. It's like a window opening. I thought I would try curtains of a heavy fabric. My rooms on the first floor forever seem to be cold. I thought I would try and keep the heat in the room where more time is spent instead of letting it escape through the opening. The room just the other side has a 20' ceiling and I know that heat rises.

so it's a horizontal rectangular-shaped opening? 100" WIDE and 41" tall?

is it like a pass-through?

where on the wall is the opening? like how high up from the floor is the bottom of the opening?

now i'm thinking that any kind of drapery would look wierd. maybe the best thing would be to install clear glass there, so you wouldn't block light.