I have a situation where half my house has cathedral cielings and they are not that well insulated. When the sun is out, even on a cool day, this will heat up the house quite a bit.

So; the heating of the roof is causing more of the heat than the outside temperature. Not running the air will always be more efficient since the outside air is providing cooling relative to the inside of the house.

For me, it works most efficiently if I keep the thermostat high during the day, and lower after the sun goes down.

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Numbers are not case sensitive. (me)