Launch an external temperature sensor for the Smart Radiator Thermostats
I'm very happy with Tado overall, apart from the performance of the Tado Smart Radiator Thermostats. I’m finding that due to the way the Tado Smart Radiator Thermostats work, they heat up a room very, very slowly, and sometimes fail to get a room anywhere near the desired temperature. I've noticed that after they turn on the radiator, they seem to then quickly turn it off as it thinks it’s reached the target temperature, when in fact it hasn’t and it's just due to the proximity of the temperature sensor to the hot radiator.
I performed a test with the bedroom in our house, it’s a simple rectangular room, measuring about 3 x 3.5 meters with a single radiator. The doors and windows were kept closed throughout:
The room was at 19ºC at 11:30 am and I set Tado to heat it to 22ºC.
The radiator heats up, but the SRT temperature sensor quite quickly reads 22ºC so Tado turns the radiator off. However, the room is actually only at 19.5ºC (measured on a 2nd thermometer elsewhere in the room), right next to the radiator it is 22ºC but not elsewhere in the room.
You then have to wait for the temperature by the radiator to cool down (about 30 mins), before the radiator will eventually heat up again, but then the whole cycle starts over again with the radiator quickly shutting off.
This means it takes a very long time for the room to get to the target temperature (and sometimes not at all), as the radiator keeps getting turned off before the room temperature is anywhere near the target temperature.
After 6.5 hours the room had still not reached its target temperature of 22ºC and is only at 20.5ºC at 6 pm, because Tado kept prematurely turning off the radiator.
Please see this graph:
Which shows the 22ºC target temp in green, the actual room temperature (measured by another thermometer at another point in the room) in orange, and the Tado graph showing it constantly turning the radiator off.
You can see from the graph that this isn’t simply solvable by setting a “Temperature Offset” in the app, as when the radiator isn’t warm the Tado thermometer more accurately represents the room temperature (and is often actually under-reporting it, not over).
However, to see what would happen, I went ahead and set an offset. As the Tado was effectively over-reading the temperature by about 1.5ºC, I set an offset of -2ºC. I then left it for over 2 hours to settle, and this was the result:
As you can see, an initial boost helps gradually raise the actual room temperature, but as it still quickly turns off the radiator, the actual room temperature only reaches about 21.3ºC, still not even close to the 22ºC target.
A side effect of this offset was that the next morning, when the radiator had been off overnight, Tado thought the room was at 16ºC when it was actually at 19ºC, and caused it to needlessly turn on the radiator. So as you can see adding an offset doesn’t solve the issue and actually introduces more problems.
In my opinion, the SRTs need to be much, much cleverer, learning the characteristics of the room and then ignoring any initial overshoot in temperature to allow the actual room temperature to get to the correct level.
Either that or Tado need release a small, cheap (~£30) temperature sensor that can be placed in the room away from the radiator to give much better results. I know you can use a Tado Smart Thermostat, but at £100 these are too expensive to put in every room.