Should I Leave the AC On When Not Home?

When It Makes Sense

• Good fit: You live in a hot or humid climate and are leaving pets, plants, or heat-sensitive items such as electronics, musical instruments, or artwork at home. A moderate indoor temperature and lower humidity can reduce the risk of overheating, mold growth, warping, or equipment damage.
• Good fit: You will be gone only a few hours and want the house comfortably cool when you return. Raising the thermostat by several degrees rather than shutting the system off can save energy while still allowing quick recovery to a comfortable temperature.

When You Should Avoid It

• Warning sign: The weather is mild or dry and the house is empty. In those conditions, running the AC continuously wastes electricity and adds unnecessary wear to the compressor and fan with little comfort or safety benefit.
• Warning sign: You are leaving for an extended trip and your system is old, poorly maintained, or prone to freezing up, leaking, or electrical issues. An unattended unit that malfunctions could cause water damage, higher repair costs, or even a fire hazard, so a full shutdown or a professional inspection may be safer.

Pros and Cons

Pros

• Keeps indoor temperature and humidity stable, which can protect sensitive occupants, pets, plants, and belongings from heat-related stress or moisture damage.
• Prevents the house from becoming uncomfortably hot, so you return to a livable space without waiting for a long cool-down period.

Cons

• Increases electricity consumption and utility costs, especially if the unit runs at a low temperature all day while no one is home.
• Adds runtime hours to the air conditioner, which can accelerate normal wear and may raise the chance of a breakdown during your absence.

Decision Checklist

• How long will the house be empty, and how hot or humid will it get outside during that time?
• Is anyone or anything staying behind that is vulnerable to heat, high humidity, or poor air circulation?
• Can you use a programmable or smart thermostat to raise the setpoint automatically, or is the system reliable enough to leave running unattended?

Alternatives to Consider

Instead of either leaving the AC fully on or turning it completely off, most households benefit from a middle path. Raise the thermostat to around 78–85°F (26–30°C) while you are away so the system runs less but still controls humidity. A smart or programmable thermostat can restore a cooler temperature shortly before you return. Closing blinds, curtains, and shades reduces solar heat gain, and using ceiling fans or a standalone dehumidifier can improve comfort without overcooling the whole house. If humidity is the main concern, a dehumidifier alone may use less energy than the AC. For extended absences, consider a pre-trip HVAC inspection and ask a trusted person to check on the house periodically.

Final Recommendation

For short errands or workdays in warm weather, raise the thermostat rather than shutting the AC off, especially if pets, plants, or humidity-sensitive items are left behind. For mild weather, short trips, or well-insulated homes, turning the system off or using setback mode is usually the more efficient choice. For extended travel or aging systems, have the unit inspected and either shut it down or set it to a conservative temperature with someone checking in. If you are unsure about equipment safety, energy costs, or insurance implications, consult a licensed HVAC professional and your utility provider for guidance tailored to your home.