It's 100+ here in Texas. My house has separate air conditioners for upstairs and downstairs. We rarely go upstairs, but I'm told that we have to account for air flow "chimney effect" up the stairway (which is not blocked off). Convection effect draws air continually up the stairway. Setting the upstairs thermostat more than 2 degrees above the downstairs thermostat means that the downstairs unit works twice as hard because it is trying to cool both spaces. Does this really happen?
Also, I'm told that I should not block off the stairway - which I could do - because it will create an "attic effect", causing the upstairs to smell bad. Can I set the downstairs to 78 and upstairs to 84? Would it make a difference in my energy bill? - Mac