Smart radiator thermostats

With a heating plan, around 10 per cent of your heating costs, according to co2online. As a rule of thumb, every degree less saves around 6 per cent of heating energy. How much it is for you depends on how often you're out and how you heat at the moment. For a poorly insulated 70 m² flat, Stiftung Warentest (issue 9/2023) reckons on around €100 a year. Work it out for yourself in the calculator below.

Without a hub is the easiest start: unpack, connect to Wi-Fi, done. That suits you if you only want to control a few radiators and it should be cheap. With a hub you pay a bit more once, but you get the thermostats that do best in tests. You can also add window contacts or a wall thermostat later. That's worth it above all if you want to fit out the whole flat.

Wi-Fi uses more power than the radio types that thermostats with a hub use. Important: your router needs 2.4 GHz Wi-Fi. That's the case with almost all routers.

Almost all normal radiator valves. Most have an M30 x 1.5 standard thread, and all the models here fit on that. For other valves, for example from Danfoss, adapters are often included, or you can get them for little money. For underfloor heating, on the other hand, you need a room thermostat on the wall.

Usually yes, because you don't change anything permanently. You just unscrew the old dial and screw the new thermostat on. You don't have to drain any water, and you don't need a tradesperson either. Keep the old dials safe and screw them back on when you move out. If in doubt, have a quick word with your landlord.

No problem: you briefly turn the thermostat up or tap warmer in the app. From the next point in your heating plan, everything runs by itself again. Some systems even use your phone's location to tell when you're on your way home.

Not if you turn it down to 16 to 17 degrees instead of right off. It shouldn't drop below 16 degrees: otherwise the walls cool down, moisture settles on them, and the risk of mould goes up. Heating the flat back up afterwards costs less than heating it all day long.

Most of the picks here notice when the temperature suddenly drops while you air the room, and turn down for a while. The Bosch thermostat needs a window contact for this. So you're not heating the outdoors.