What's the real cost of running AC all night in a rental property?

A split unit running overnight at 16°C uses up to 70% more electricity than at 24°C. Across a peak season, that overnight waste costs rental operators €150–250 per room, and that is before accounting for daytime waste when guests are out.

Why overnight AC waste is the most expensive pattern in rentals

Guests arrive, cool down from the heat of the day, and set the AC as low as the remote allows. By the time they fall asleep, the room is already cold. The unit keeps running at 16°C for seven or eight hours through the night, drawing maximum electricity to maintain a temperature nobody consciously chose, they were already asleep when the room reached that point.

This pattern is not unusual. It is the standard. Across thousands of holiday rental stays, guests rarely adjust overnight settings. The remote is on the bedside table; the default is whatever they set it to in the evening.

What makes this expensive is not just the temperature. It is the combination of three factors:

• Continuous operation at maximum cooling demand through the longest uninterrupted block of the day
• Low ambient temperatures at night, which force the unit to work harder to maintain a large differential
• No interruption, guests are asleep and will not adjust the remote until morning

That seven-to-eight hour block is often the single most expensive period of AC usage in any 24-hour rental day.

The 70% figure: what it means in practice

IEA and EU building energy data consistently show that extreme AC setpoints, particularly settings below 20°C in ambient temperatures above 25°C, increase electricity consumption by 30–70% compared to a 24°C setpoint. Guests who set 16°C can increase AC energy use by up to 70% compared to a 24°C setting.

That figure is often cited in energy policy contexts. What it means for a property operator is more concrete:

The practical effect: an operator running ten rooms where guests consistently sleep with AC at 16°C pays materially more overnight electricity per night than an operator whose rooms default to 24°C, not because of a different unit or a higher tariff, but because of a remote control setting nobody thought to change.

What overnight waste costs per room, per season

The economics are straightforward. If a unit uses significantly more electricity overnight at 16°C than at 24°C, and if that pattern repeats across a 100-to-120-night peak season, the cost difference per room is substantial before any other factor is considered.

Overnight waste accounts for a significant portion of the €190–450 per unit per season that Narveo operators typically recover. The remainder comes from daytime waste, units running continuously while guests are at the beach, at lunch, or on day trips.

Neither pattern is intentional on the guest's part. Both are a direct result of AC systems that have no way to limit unnecessary runtime or prevent extreme setpoints.

Why guests set 16°C at night

Guests do not set 16°C because they need the room to be 16°C. They set it because they are hot after a day in the Mediterranean sun, they want results immediately, and they assume the unit will reach a comfortable temperature and stop. In many domestic contexts, that assumption is partially correct, a programmable thermostat will cycle on and off around a target. In a standard holiday rental with a basic split unit and a handheld remote, the unit runs continuously at whatever setting was chosen.

By the time the guest is asleep and the room is already cold, the unit is still running at 16°C. No one turns it up. No one turns it off. It runs that way until morning.

This is not a complaint about guest behaviour. It is a structural feature of how split AC systems work in rentals: the incentive to adjust is zero, the friction to adjust is low but non-zero, and the default is to leave it.

What actually stops overnight waste

Behavioural approaches, house rules, welcome book guidance, reminders at check-in, do not change overnight patterns in any meaningful way. Guests cannot be expected to remember an energy message from hours earlier while half-asleep at 2am.

Occupancy sensors shut off AC when no movement is detected. In a bedroom, guests are asleep and stationary. Sensors read an empty room and cut the AC mid-sleep. Guests wake up hot, override the system, and leave a negative review.

Minimum temperature limits and automatic runtime control address the actual problem. If the AC cannot be set below 21°C, overnight consumption at the extreme end is eliminated. If a runtime limit resets after a set interval, continuous unattended operation through the night is capped without interrupting active use.

Narveo applies both. No WiFi, no app, no installation. The unit is set once by the operator; guests retain full access to cooling.

White paper

Thermostat setpoint optimisation in split air conditioning systems: a physics-driven framework for energy reduction

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When Narveo is not the right solution

Narveo works best in warm-climate rentals where split AC units run continuously through a four-to-six month peak season. Properties in cool climates, or where guests rarely run AC overnight, will see a proportionally smaller return. Narveo is not compatible with ducted central air or centralised building management systems. It is also less suited to owner-occupied properties where the owner is present to manage their own usage.