Thermostats are made for a multitude of applications. The most basic
ones are millivolt or 24 volt.
Millivolt Thermostats: Used widely for
certified heating appliances like gas wall heaters (that do not have a
blower), and gas fireplaces/stoves. The standing pilot generates
enough power to operate the gas valve and the millivolt thermostat.
So even if the power goes out (common in Tahoe).
Remote Controls: Work with millivolt
systems and are especially handy for controlling gas fireplaces when
running a thermostat wire is impractical (like thru rock).
24 Volt Thermostats: Used for Forced Air Units
(furnaces), Wall heaters that have fans, boilers, or any heating appliance
that is connected to power from the breaker box.