What is UL's concern/requirement that power fans each have a dedicated thermostat controller (or thermostat/humidistat controller) as opposed to wiring two power fans to one?

UL requires 1 controller per power fan due to amp draw concerns.

The concern (and real issue) is the amp draw for two motors running through the same switch which is only rated to handle one motor. If the switch was only used on a 24V control circuit and the supply power to the motors was run through a relay it would not be an issue. However, power for the fans runs through the switch, leaving us limited to one switch per power fan.