Connect ONLY one heater by using the below:
A double pole thermostat will have 4 connection points.
Two of them, will be labeled either LINE or L1 and L2
That is where you connect both of the wires from the circuit breaker
, one to each of the connections.
The other two connections will be labeled either LOAD or T1 and T2.
The 2 wires to the heater are connected to those points, one to each.
That is pretty much it, except for the ground wire at the heater and thermostat if the thermostat has a ground screw.
NOW, connect the 2nd heater to the SAME thermostat points as the first heater, one wire to each of the points.
That is parallel, when they connect together and to the same points
Questions, just reply.