I said I was going to do this, but didn't; until yesterday. Sustained subzero temperatures finally got me to put the plastic up over the entrance to the largely unused great room. I have the vents half-opened in there, so it won't be too cold, but the main reason for closing it off is to keep the heat IN the kitchen. That vast, vaulted space swallowed the heat from the kitchen with a loud sucking noise. Yesterday morning it was 49 degrees in the kitchen, although the thermostat was set at 63 overnight. This morning it was 60 degrees in the kitchen. Hurrah!
Who' d of thought it would come to this!