When if comes the programmable thermostats there are two major types
Line voltage and low voltage programmable thermostats, it’s very important you know which type you need before you purchase a new thermostats
A line voltage system uses direct current instead of only 24 volts which is also know as “ low voltage” line voltage used direct current. The direct current will be either 120 or 240 volt electrical line most commonly used for electric heaters or a direct-wired electric furnace.
Still confused, no problem in the simplest of terms a line voltage thermostat is connect to a two or three romax wire that will be either 14, 12, 10 or 8 gauge in think thickness. And low voltage thermostat will use 24v bell wire is much smaller is size so you will be able to tell very quickly if you are taking an old thermostat off..
To go into more detail if we start from your “fuse box or “circuit breaker panel” the electrical wire from the panel to your heater will be 120 or 240 volts and the wire is measured in gauge thickness starting at 14 gauge to 8 gauge and once you electric wire gets to the heater you will need another wire to connect to your thermostat. A line voltage thermostat will use the same type of wire from the heater to the thermostat a low voltage thermostat will go through a transformer and a relay which knocks down the power from 120 of 240 volts down to 24v. A 24v wire is what is called “ bell wire” its very thin and you will be able to tell the difference between 120 and 240 volt wire and once the wire goes from the heater to the thermostat
Because line voltage programmable thermostat are most commonly used for electric heaters it is very important if you are looking to reduce your energy bills to get a digital and or a digital programmable thermostat, the main reason being is a digital thermostat has a better sensor inside it which reads the current air temperature when the sensor reads the temperature you what the room to be at it will send a single to turn the heater off. An older thermostat will have a sensor that will not work as well and it may not read the correct, and the unit shut off as fast which lead to larger utility bills. Another key feature with a digital programmable thermostat is its great for the absent minded. Its has a clock inside the unit so you can tell it at what time you want the current temp to be, so for those hours you are at work or school or sleeping you can set it to lower automatically