A/C operation question?

Not enough info.
Maximum efficiency and lower energy use can be very different things.
In general, upping the temp a few degrees will also slow down heat transfer between inside to outside. That is how energy is saved.
The equipment itself is generally most efficient when running non stop but that may depend on your ducting and other things.

HVAC’s generally speaking don’t have different settings, they are either running or not running. So turning the temp to where the machine has to run less to maintain an easier temp is fairly obviously less energy.

As an example, to maintain 68 it may have to run 50 mins an hour, 70 maybe 40 mins an hour, and 72 maybe 30 mins an hour.

Its going to be a guess without measurements but I'd say this one:

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B) Turn up to 78 during day when nobody is home and 72 at night

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easier than warming it up then cooling it down a bunch,

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easier on what though?

Even if you have if you have a box with 10feet of closed cell foam in its walls, its still going to be more energy efficient to let the temp rise in the day. It will be an minuscule amount but it will still be an amount.


But if you're uncomfortable in your home then you need to re-evaluate your temp setting. After all, comfort is the primary purpose of conditioning the air.

Thermodynamics says:

Turn up to 78 during day when nobody is home and 72 at night

Requires less energy. Why not 80 during the day and save more?

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When first bumping it up to 75-76 in the AM, the a/c is at rest for a minimum of 3 hours.
In evening, when putting down to 71, it doesn’t take 3 hours of constant running to get back down.

So the 3plus hour break in the mornings saves $$$.

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this isnt perfect math though


if you left it on 71 in the morning, it likely wouldn't have to run very much during that ensuing 3 hours, so by allowing the temp to rise from 71-76, you have saved way less run time than 3 hours

it would also depend on the amount of minutes per hour it would take to maintain 71 vs 76


I still think its cheaper to raise the temp, just saying your math isn't correct

You also have to throw in how tight The house is. If you’re bringing in a lot of humidity, the unit is going to have to work to remove that humidity and that percentage of the work isn’t being used to draw the house temperature down. What the trade considers a properly sized house, there is little excess capacity to bring the house temperature down fast enough to support the original point of the thread.