Our XLS and iQ ranges work slightly differently from each other but in summary it is possible to pair multiple panels to one thermostat, as follows:
Herschel Select XLS Range
T-MT, T-BT, T-PL
You can pair multiple Heater Panels to a single thermostat using the standard pairing procedure on the panel instructions.
Herschel iQ Range
MD2, T-MKS, T-MKW
Up to 16 amps of heater load can be directly wired through the MD2. If the overall heater load to be controlled by the MD2 exceeds 16 amps, then an appropriately sized contactor must be used to handle the heater load and the MD2 just switches the contactor.
Multiple R2s can be paired with a T2.
Up to 10 amps of heater load can be directly wired to an R2.
Where overall heater load exceeds 10 amps, you could use a contactor (as MD2 above), but it is probably more pragmatic to use multiple R2s and just pair these to the T2.