Drolet Heat Commander Installation And Operating Instructions Manual page 38

Example of thermostat wiring:
Connect one wire to "RH" and the other wire to "W". The red jumper can be left in place. For
more information, refer to the manufacturer's instructions.
This furnace may be installed in parallel as an add-on to an existing furnace in the USA only.
Such an installation requires that the furnace's controls be interlocked to prevent both
furnaces from heating at maximum rate simultaneously.
There are two ways to connect the existing thermostat to your device:
1- From the terminal of the existing furnace, connect 2 new wires (B) to the existing wire
(A) and fix them to the terminal identified "I" (interlock) of the parallel Add-On furnace.
PARALLEL
ADD-ON
EXISTING
FURNACE
FURNACE
USA only