What is better: to turn off my AC when I leave my home for 3 days and then turn it on when I come back, or just increase the temperature?
I suspect it is better to increase the temperature, but I'm not quite sure.
In San Antonio, TX, I would suggest turning up the temperature.
- The issue is not just energy savings, but includes moisture management too. High moisture typically comes with high temps and is not good for a house or its contents. A/C manages moisture too.
- Of course in three days nothing should be affected by moisture, but why take the chance?
As far as which method is cheaper from an energy perspective, it is very hard to accurately answer that question. The answer depends on a number of variables, including the
- quality of construction (insulation, windows, etc),
- efficiency and sizing of the A/C systems,
- exposure to sun/shade,
- orientation of the house and windows to direct sun,
- daily outside temperature, etc.
In general, it is probably going to be cheaper to turn the system off and restart when you get back, especially if the A/C systems are properly sized for the house.
For more information:
Read Steve Saunders's Q&A "Does a programmable thermostat really save 20% on my utility bills?"
And, check Cynthia Phakos's Q&A "Is it better to turn off the AC during the day, using it only at night, or to keep it on day and night?"