Choosing a smart thermostat for a flat: what to check first

What kind of heating system your flat actually has

Most Tallinn flats are on district heating (kaugküte), where hot water runs through radiators or through pipes in the floor, and the room thermostat controls a valve rather than a boiler. Newer developments often have underfloor heating with a manifold in a cupboard, each loop controlled by its own actuator. A handful of older buildings still have electric storage heaters or electric underfloor cables, which is a different wiring problem altogether.

The heating type decides what the thermostat needs to control. A radiator valve wants a small battery-powered head that turns a pin, wired underfloor heating wants a wall thermostat switching a relay or actuator at the manifold, and electric underfloor heating wants a thermostat rated for the wattage of the cable, usually with its own sensor probe in the floor.

If you are not sure which you have, look at the manifold cupboard for underfloor loops with numbered valves, or check whether your radiators have a simple two-pipe connection with a manual valve head that you could swap for a smart one. A flat with a mix of both needs a different device for each.

Whether there is a neutral wire behind the thermostat

Most smart thermostats that plug into mains-style wiring need a neutral wire (N) at the wall unit to power their screen and Wi-Fi radio continuously. Many Estonian flats, especially older panel buildings, only ran a switched live and earth to the old mechanical thermostat, with no neutral present in that back box.

Some smart thermostats are built to work without a neutral, drawing a trickle of power through the switched line itself, but they are pickier about which heating systems they pair with and occasionally cause slight flickering on other loads on the same circuit. Battery-powered radiator valves avoid the question entirely, since they only need to turn a pin, not run a screen.

Open the existing thermostat's back plate before you buy anything, or ask us to check it. If there is no neutral and you want a mains-powered model, running one usually means opening a short stretch of wall or chasing a cable to the nearest distribution board, which is electrical work best left to a qualified electrician — from 49 € an hour, call-out included in the first hour if the job goes ahead.

Actuator, relay contact or direct line — the type of connection

This is where most returns come from. A radiator thermostat with an actuator head turns a small pin on the valve body and takes a specific thread size, so measure the existing head before ordering — M30 x 1.5 is common but not universal. Underfloor heating manifolds usually have actuators on each loop wired back to a relay box, and the smart thermostat needs to speak to that relay box, either directly or through a hub.

A dry relay contact simply switches a circuit on and off, which suits a boiler or a pump but tells the thermostat nothing about the actual water temperature reaching the floor, so some systems pair a wall sensor with the relay for better accuracy. A direct line, where the thermostat itself carries the switching current, is simpler to wire but less common in shared-building heating setups.

Before buying, find the manufacturer's compatibility list and match it against what is in your manifold cupboard or on your radiator, not just against "underfloor heating" as a general category. If the listing does not name your actuator or relay brand, treat that as a real gap, not a formality.

• Radiator valve: check the thread size on the existing head
• Underfloor manifold: count the loops and note the actuator or relay brand
• Relay contact: confirm whether it is dry-contact or carries live voltage
• Electric underfloor cable: check the wattage rating matches the thermostat
• Take a photo of the open back plate before you order anything

Choosing the app and smart home ecosystem

Once wiring and connection type are settled, the app is the easy part, but it still decides how much the thermostat can actually do. Most brands run their own app for scheduling and away detection, and separately offer varying levels of support for Apple Home, Google Home or Matter, which matters if you already run other smart devices and want one control point rather than four apps.

If you rent, or if the flat is part of an apartment association managing shared district heating, keep the setup simple: a thermostat that works fine from its own app without depending on a hub is easier to hand over or explain to the next tenant. If you own several devices already and want scenes — heating dropping when you leave, rising before you're due home — checking Matter or Thread support saves you from being locked into one brand later.

Wi-Fi coverage at the manifold cupboard or by the radiator is worth testing before you commit, since cupboards behind concrete walls are a common dead spot in panel buildings and some thermostats need a stronger signal than a phone does.

When to try it yourself and when to call for help

Swapping a battery-powered radiator valve head is a job most people can do in ten minutes with no tools beyond what comes in the box, provided the thread matches. Pairing it to an app is the same as any other smart device setup.

Once you're dealing with a back box behind a mains thermostat, an unclear neutral, or a relay box at the manifold that needs opening, it stops being a weekend project and starts being electrical work, both because of safety and because a wrongly wired relay can leave a whole loop either permanently on or permanently off through a winter.

We do smart home installation as a fixed-price job from 90 €, which covers checking your wiring, confirming compatibility before you buy anything, and setting the thermostat up in its app. Straight electrical work, such as running a neutral wire or rewiring a relay box, is billed at 49 € an hour with the first hour as minimum.