If you search for "smart thermostat" you will mostly see round or square devices that screw to the wall and run the heating and central air of a house. They work very well in the United States or in Europe. In Medellín they almost never have anywhere to connect.

The reason is simple: here most houses and apartments do not have a central air or heating system. What there is, when there is something, is a minisplit in a bedroom, a fan, a water heater, or, on cold-country farms, an electric space heater. None of those are controlled with traditional thermostat wires.

That does not mean you cannot automate temperature. It means the "thermostat" is built differently.

First check what you have

Before you buy anything, look at what equipment you want to control:

• Central air or fan coil with a wall thermostat. This happens in some new buildings, offices, and large homes. Here a replacement smart thermostat does apply, as long as it is compatible with the wires and voltage of the thermostat you already have. Take a photo of the wires before you disconnect and compare it with the maker's compatibility list.
• Minisplit with a remote. This is the most common case. It has no thermostat wires; it is controlled with the infrared remote or with the brand's own Wi-Fi module.
• Ceiling or standing fan. It is controlled by the switch, by a plug, or by the remote if it has one.
• Electric space heater. It is controlled by cutting or giving it power, carefully because of the load it draws.

Depending on what comes out of that list, the solution changes.

For a minisplit: sensor plus control

With a minisplit, the smart thermostat is really two pieces:

1. A temperature sensor in the bedroom, away from the air, at bed or sofa height. The sensor built into the minisplit measures the air that enters the unit, near the ceiling, and that is why the bedroom often feels different from what the unit says.
2. Something that gives orders to the minisplit: the brand's Wi-Fi module, a universal infrared controller, or a module that connects straight to the unit's board.

With those two pieces, a rule in Home Assistant does the thermostat's job: if the bedroom goes past a certain temperature and someone is there, it turns the AC on; if it drops, it turns it off or switches to fan. We cover the control options in universal control for air conditioning and the fuller version, with a module inside the unit, in improve a minisplit with ESP32 and Zigbee.

Choosing the sensor

For temperature almost any small battery Zigbee or Matter sensor works. What is worth checking:

• That it also reports humidity. In Medellín how hot it feels has as much to do with humidity as with degrees, and the minisplit's "dry" mode sometimes solves more than lowering the temperature.
• That it works locally. Zigbee or Matter over Thread, so the rule keeps running even if internet drops.
• Where you put it. Not in the sun, not next to the window, not under the AC. A shelf at mid height is usually the best place.

We talk about these sensors in detail in presence, temperature, and humidity sensors, and about why we prefer Zigbee and Thread in Zigbee and Thread at home.

Knowing if someone is there

A thermostat that only looks at degrees cools empty bedrooms. What saves the most is adding presence:

• A presence sensor in the bedroom that turns the AC off when nobody is using it.
• A window sensor that turns it off if someone opens for the breeze. See door and window sensors.
• A simple schedule: that the bedroom is cool a while before sleep and turns off on its own in the early morning, when Medellín cools down.

If you want to know how much the AC really uses in your home, a consumption meter shows it in the app. We cover that in electricity consumption monitoring.

Fans and heaters

For a fan, the rule is the same as with the minisplit, but the command goes to a smart plug or a smart switch. If the fan has a remote, a universal controller also works.

For an electric space heater, for example on a farm in Santa Elena or in Oriente, check how much current it draws before you put it on a smart plug. Many plugs cannot handle a heater's load continuously. In that case a high-capacity relay installed by an electrician is better, like Shelly's, and always leave the heater's own thermal protection working on its own.

When to buy a wall thermostat

If your building has central air or fan coils with a wall thermostat, swapping it for a smart one can be worth it. Before you buy:

• Confirm that the model is sold or can be shipped to Colombia and that it works with the voltage and wires you have.
• Ask building management if you can change it; in some buildings the system is shared.
• Prefer one that integrates with Home Assistant or with Matter locally, so you do not depend only on the brand app.

Where to start

For most apartments in Medellín the order is this: a temperature and humidity sensor in the bedroom where the AC is, a control for the minisplit, and a simple rule with presence. With that you already have what a smart thermostat does, without changing anything on the wall.

If you do not have AC yet and are thinking whether you need it, start with air conditioning in Medellín. And if you want to see what makes sense for your home in general, the smart home test takes a couple of minutes. For the full picture, see home automation in Medellín.