I'm surprised that I can't find more useful information on this. I have a split level home. Main floor contains living dining and kitchen. 8 stairs up to top level with 3 bedrooms and a bathroom. Down 6 steps from main level to family room and from there down another 6 steps to fully underground sub-basement. My last house was a ranch which we liked to keep warm at about 75F or so in the winter. With the thermostat set to 75 in the current split level, the top level must be 90F if not higher. The thermostat is in the dining room next to a sizeable window. I just covered the "out" vents in the top level but I'm not sure if this is safe/efficient/productive, etc. The bottom 2 levels have electric floor heating in addition to vents from furnace. Furnace is in sub-basement.
Any suggestions greatly appreciated.