During the setup process (app.themo.io/setup) you will be prompted to select installed temperature sensor. 

Themo comes equipped with NTC 10 kOhm temperature sensor. If this was used during the installation, then select 10 kOhm from the dropdown menu (default value).

Themo also support various other temperature sensors such as:

NTC 6,8 kOhm 

NTC 12 kOhm 

NTC 15 kOhm 

NTC 33 kOhm

NTC 47 kOhm

If during the installation the existing temperature sensors was used, then the closest value to the installed sensor has to be selected from the dropdown menu.

If exact value of temperature sensor is unknown then select the one that is indicating the temperature that corresponds to the actual temperature off your floor. If no other means are available, just touch the floor with your hand and choose the sensor which is indicating the closest temperature in your opinion. You can later change your temperature sensor via re-setup.

How can I re-do the setup process?.