Air Conditioning on Vacation: Leave It On, Turn It Off, or Set It to Eco Mode?

You’re almost ready to leave for vacation, and once you’ve closed the front door, you always ask yourself the same question: What should you do about the air conditioner while you’re away? Should you unplug everything to save as much as possible? Leave it running on low so you don’t come home to an oven (or a freezer, if it’s winter)? Or trust the eco mode and leave with peace of mind? The right answer depends on how many days you’ll be away, the type of unit you have at home, and what you value most—immediate savings or comfort upon your return. Let’s get right to the point.

Air Conditioning During Vacation: What Really Changes in Energy Consumption

Before deciding what to do with your air conditioner while on vacation, it’s worth distinguishing between two concepts that are often confused: being plugged in (on standby, ready to receive commands from the remote or app) and being in operation (compressor running, cooling or heating). These are very different in terms of energy consumption.

A unit on standby—with the display light off or just the clock on, waiting for a command or a Wi-Fi signal—typically consumes very little power, in the range of 1 to 3 watts. Over the course of a two-week vacation, that amounts to cents, not euros. However, an appliance running to cool or heat an empty house is a different story: in that case, energy consumption rises in proportion to the hours of operation and the difference between the outside temperature and the temperature the appliance is trying to maintain inside.

In other words: unplugging the air conditioner before going on vacation doesn’t result in significant savings compared to simply leaving it on standby. The decision that really matters is whether you’ll leave it running (in eco mode, with a timer, or a thermostat) or completely turned off.

Eco mode and timer: the balanced option for short absences

If you’ll be away for two or three days—a long weekend, for example—turning everything off may not be worth it: when you return, the unit will need to work harder to restore the comfortable temperature, and that startup phase is always the most energy-intensive. In these cases, it makes more sense to:

1. Set the unit to Eco mode (or a higher temperature in cooling mode, typically 26–27°C, or a lower temperature in heating mode) instead of turning it off completely;
2. Set the timer or app to further reduce operation during the hours when no one is home;
3. If the unit has Wi-Fi (such as the kit included in many current residential models), open the app a little before you arrive, so you’ll find the house already comfortable without it having run at full capacity all day;
4. Close the blinds and curtains on the side most exposed to the sun to reduce the heat load that the unit then has to compensate for.

This works particularly well with units featuring inverter technology, which nowadays make up the overwhelming majority of air conditioners sold in Portugal. Unlike older units, which turn the compressor on and off in complete cycles (resulting in more abrupt and less efficient starts), an inverter continuously adjusts the power output—which is why eco mode can keep a home comfortable with much more controlled energy consumption than the technology from a few years ago.

Long Vacations: When It Makes Sense to Turn It Off Completely

For longer absences—one or more weeks, as is common in the summer—the equation changes. Keeping the air conditioner running, even in eco mode, in a locked-up house with no one inside for two or three weeks tends to cost more than the comfort gained upon arrival, especially if the house is well-insulated and there is no heat-sensitive equipment (such as certain electronic devices or instruments) that requires a controlled temperature.

In this scenario, the most common recommendation is simple: turn off the air conditioner (no need to unplug it, just stop it from running) and, if possible, leave a window slightly ajar with a mosquito net in a shaded room, to allow some air circulation without letting strangers into the house. In homes with a history of dampness—basements, ground floors, areas near the sea or rivers — it’s worth considering a short, scheduled dehumidification cycle for the last few days before your return, precisely to prevent that musty smell and the risk of mold on fabrics and walls.

A real-world example: what we recommend to a residential customer

A real (and common) example we’ve seen many times with clients: a single-family home in the Famalicão area, equipped with a wall-mounted single-split unit featuring DC Inverter technology, eco-friendly R32 refrigerant, energy class A++/A+++, and a SEER of 6.1—specifications typical of residential units currently installed by LEFE, such as the NIPON VITA12 model used in this case.

For a two-week absence in August, the recommendation was to turn off the unit completely, since the house has good blinds (which reduce direct solar gain) and no heat-sensitive equipment. As for weekend getaways throughout the summer, the suggestion was to keep the eco mode with the timer enabled via the app, activating the unit about 30 to 40 minutes before the expected arrival time — enough for a single-split unit of this capacity (3.2 to 3.4 kW) to restore a comfortable temperature in a medium-sized room without having to run all weekend.

On, Off, or Eco: A Quick Comparison

Conclusion

There’s no one-size-fits-all answer to “on, off, or eco”: it depends on how long you’ll be away and the specifics of your home. For short getaways, eco mode with a timer (or the unit’s app) is usually the best balance. For long vacations, turning it off completely is usually the most sensible option—especially with modern inverter units, which restore a comfortable temperature much faster than units from a decade ago. The rest—closed blinds, a clean filter, and a dehumidification cycle on the last few days—are small details that make the difference between returning to a comfortable home or one that will still take the whole afternoon to “settle in.”