Electric Baseboard Heater Thermostat Replacement
Any thermostat rated at or above the heater ratings should work fine. 3600W is a good number because that is 15A @ 240V, which is also a common breaker size. My guess is that the original installer used the same thermostats everywhere, costing a little more but minimizing the number of inventory items. 3600W/15A also allows you to upgrade a bit in the future without replacing the thermostat.