Line Voltage Thermostats

Line voltage thermostats, which may be programmable, are directly wired to the baseboards or radiant heat systems. They are also often unreliable, and are not recommended for other types of heating systems.

A variety of thermostats are available for a wide range of budgets. For programmable thermostats, look for an Energy Star model to make sure you are maximizing energy savings. Also, if you are replacing an old thermostat, it probably contains mercury and cannot simply be thrown in the trash. Find a mercury recycling program in your area.

Source: http://www.networx.com/article/compare-thermostat-types