I have a theoretical question.
Facts: 2,600 sq ft house in NE Oklahoma (2,300 down, 300 upstairs game room), two separate heating and cooling units, the upstairs is connected to downstairs via a closed-sided stairway with a doorway at the bottom of the stairs (no door or open railing).
Assumption: In the winter season, heated downstairs air will rise up the stairway, creating a heat loss to the downstairs.
Keep in mind that I am most interested in climate control downstairs and am wondering how the furnace usage upstairs will affect the downstairs temperature.
The question is: If the upstairs heater was run sparingly (keeping the upstairs cooler), A) would the downstairs heat loss be less because cool air would fall down the stairs and suppress the heated air trying to rise up the stairs OR B) would the falling cool air overpower the rising heated air causing the downstairs to cool off, which would make the downstairs heater run more OR C) would heat from downstairs rise up the stairway (and be lost to the downstairs) no matter how cool it is upstairs?