INSTEON Wireless Thermostat with Humidity (2441ZTH) Quick Start - Manual (Page 7)

You can control vintage millivolt heaters with
the INSTEON Wireless Thermostat if you
replace the mercury float or battery-powered
thermostat with an IO Module*.
*Wireless Thermostat requires at least one
Dual-Band INSTEON device to communicate
with IO Module.
Controlling Millivolt Heaters