Radiator valves, an unnecessarily bad design
Do you turn your radiator to its highest setting to heat the room faster?
The numbers seem to represent the power with which to heat. In reality, they represent a rough temperature range.
by Johannes Maas under CC BY 4.0It is natural to assume that the numbers represent the strength of the heating. Setting it to 5, with this understanding, will heat the room quicker, because more hot water is assumed to be pumped through. This misunderstanding is described in Don Norman’s book The Design of Everyday Things (ISBN 978-0-465-05065-9, p. 58).
In reality, the valve sets a target temperature. The 3 is around 19 °C and the 4 around 22 °C.
If the current temperature is below the target temperature, the radiator always heats as much as it can, until the temperature reaches its desired level. Setting a higher number will therefore not heat up the room quicker, it will only heat it up to a higher temperature.
How to fix it
Label the valve with the approximate temperature. Not only does it mitigate the misunderstanding of its function, it also helps choose the appropriate setting.