Before you turn on the air conditioner
Compare indoor and outdoor temperature before you switch the AC on. Outdoor air can cool the home. Ventilate does not invent a number on your bill.
Having air conditioning does not change the first question. Is the air outside actually cooler than the air inside?
If it is, opening the right windows can cool the home, and you can leave the AC off, or run it later and for less time. If it is not, the machine is doing a job outdoor air cannot do. Shade first, cool people with moving air, then cool the room if you still need to.
This is not a promise about your electricity bill. Ventilate does not estimate kilowatt hours or a saving in money. It tells you the moment when outdoor air can do the work.
Check the air, then the switch
Use an indoor thermometer away from sun and appliances. Compare it with a shaded outdoor reading, not a sensor on a hot balcony.
- Outside is warmer: keep windows closed. Shading and a fan on you still help. If you use the AC, do not feed outdoor heat in through open glass
- Outside is cooler: open where it is safe, make a path through the home, and wait. Many evenings this is enough to make the room bearable without mechanical cooling
- Outside never gets cooler: a tropical night or a top-floor room that stays hot is a reason to use AC for sleep and health, not a reason to leave windows open on hotter air
The comparison is the same as indoor versus outdoor temperature. The AC is the step after that comparison, not a replacement for it.
Why this can cut cooling use
An air conditioner removes heat that entered the home. Every hour of 35 °C air through an open window is heat you later pay to pump back out. Closing in the heat of the day, shading the glass, and flushing when outdoor air is cooler reduces how much heat the machine has to handle.
That is the whole mechanism. It is not a tariff, a smart meter, or a simulated bill.
Fans cost less to run than AC and they do a different job. They cool people, and they move air when you are ventilating. They do not replace AC on a night that never cools down. See where to place a fan and how to cool your body.
When you should still use it
Use air conditioning when:
- Outdoor air stays as warm as, or warmer than, the room
- Someone is at high risk in the heat (older people, very young children, some medications)
- Indoor temperature is already unsafe and ventilation cannot catch up
Then keep the windows closed while it runs, or you are cooling the street.
Safety first
None of this replaces medical judgement. If someone is showing signs of heat exhaustion, confusion, or heatstroke, get help. Follow your local health agency.
Ventilate ranks each window using indoor temperature, local weather, sun, and layout, so you can see whether outdoor air is ready before you reach for the remote.