Is it better to cool the whole house or just the floor I'm using?

I live in a two-story house. There are separate HVAC zones, one for the 2nd story, one for the ground floor.

Is it better (more efficient, cheaper) to just turn on the air conditioning to cool the ground floor where we are, or should we turn on both to cool the top and bottom floors?
thanks!

Answers:
It is good that you have two seperate systems, but do not turn the upstairs system off completely. When homes are built they generally do not put insulation between the ceiling of your downstairs and floor of the upstairs. Therefore if you turn the upstairs completely off the heat from upstairs will come through your ceiling downstairs because of the lack of insulation. Basically adding more heat load to the home. This will ultimatly make the downstairs system work harder to maintain the temp in the downstairs part of the home. Yes, you can set the temperature on the upstairs system higher, but don't vary it more than 5 degrees from the main floor temp.

Other answers:
They built the home with a Split system for a reason- so you can use one. If you don't use the second floor leave it off. Only problem I see is the lower AC pulling warm air from the second floor.
They built the home with a Split system for a reason- so you can use one. If you don't use the second floor leave it off. Only problem I see is the lower AC pulling warm air from the second floor.
Only cool the are that you're using. Save money and elecricity. There are different systems for a reason.
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