Use one T1 per room / zone and one R1 per heater. Each R1 requires mains electricity supply.
Wirelessly pair each R1 to the T1.
The T1 can be located anywhere in the room and is battery operated so does not require mains supply. Can be surface mounted to the wall or placed on a shelf. A great retrofit option minimising disruption to walls / ceilings because R1 can be located close to heater.
Can become App-enabled by adding the Herschel iQ hub (optional).