Line-voltage thermostats are powered directly by a standard 120-volt or 240-volt circuit—the same circuit that powers a permanent electric heater. They are primarily used for electric resistance heating systems, such as electric baseboard heaters and in-wall heaters. These thermostats are not as sensitive as most low-voltage types, and it may take a temperature fluctuation up to 7 degrees Fahrenheit to make them respond. As a result, expect wider temperature fluctuations in any heating system controlled by these thermostats.

　　

　　One way to know if you have a line-voltage thermostat is to look at the wires. The wire leads will be quite thick, 12-gauge or 14-gauge wires, like those connected to a wall outlet or light switch. By contrast, wires for low-voltage thermostats are very thin, similar to wiring for doorbells or telephone jacks. You can also check for a voltage listing inside the cover of the thermostat, or on the heat pump, furnace (inside the access door), boiler, or the electrical baseboard unit itself.

　　Number of thermostat wires: two to fourVoltage: 120 volts AC or 240 volts AC

They are commonly used with:

　　Electric baseboard heatersLocalized heating systems (with a line-voltage thermostat in each room)Oil-fired hot water boiler for radiant heat or baseboard hydronic systems