How Your Thermostat Works

There are two types of home thermostats used in home heating and cooling systems.

Introduction:

If you have a heating or cooling system in your home you have at least one thermostat. In home with multiple heating and cooling zones there is a thermostat for each zone. The thermostat's basic function is to regulate the operation of heating and cooling equipment in your home. Setting the thermostat to the desired temperature will turn the equipment on and off to maintain that temperature.

A thermostat is essentially an automatic switch. The thermostat senses the temperature in the room and turns the air conditioner or heater system on and off as to maintain the desired temperature.

There are two basic types of thermostats, electromechanical and electronic. They both do the same thing but they do it in different ways. Of the two basic types, there are several varieties from which to choose because there are many different manufacturers.

The electromechanical thermostat uses a bi-metallic coil or metal strip which moves as it expands and contracts with temperature changes. Mounted on the bi-metallic strip is a glass vial that is partially filled with mercury. As the vial becomes tilted the mercury flows to the end of the vial where there are two electrical contacts exposed. When the mercury contacts these electrical contacts a low voltage circuit is made. This works just like a light switch and makes a circuit to turn on the heating or cooling system.

An electronic thermostat works much the same way as an electromechanical except that instead of having a bi-metallic strip and mercury switch, it uses a thermo sensor to detect temperature levels in the room. When the temperature differs from the preselected temperature the thermostat electronically makes the circuit to the heating or cooling system.

Advanced features of electronic thermostats include programmable thermostats where different temperatures can pre-set for a certain time of day or days of the week. They also incorporate an additional feature called a heat anticipator. They are for certain types of heating equipment that continues to generate heat even after they are powered off. This feature shuts off the system in advance of reaching the preset preferred temperature.

That’s how your thermostat works. Most home thermostats use only low-voltage. The power still should be shut off to the heating and cooling systems at the circuit breaker when work is being performed on the thermostat. When replacing a thermostat an accidental shorting of wires may damage the equipment although it may not cause personal injuries.

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