This component is often thought of as the brain of any heating or cooling system. The thermostat is what sets the temperature in the home and keeps it from going under a certain number when heating or over a certain number when cooling. When the temperature reaches an undesired level, the thermostat begins the heating or cooling process. To better understand your thermostat, it is good to get to know its components.
These were the standard thermostats used in homes and businesses for many years. They are most easily distinguished by the lever used to slide the thermostat to the desired temperature. They also don’t commonly employ battery power and are wired into the home.
Thermometer and Mercury Switch
Functioning like the thermometers used to take someone’s temperature, the thermometers in your thermostat also use rising and falling mercury, an element that responds to changes in temperature in its liquid form. Thermostats often have two thermometers: the one used to tell the current temperature that is located in the cover, and the other is located in the top layer of the thermostat and controls the heating and cooling systems.
These strips are two pieces of metal laminated together that work in conjunction with the mercury switch. The metals expand, contract, and/or unwind based on the temperature. The center of these strips is connected to a temperature adjustment lever and the mercury switch.
How They Work Together
When the thermostat is set to heat or cool it tips the mercury switch in a certain direction, usually left for heat or right for cool. The tip allows current to flow through the mercury and make contact with a relay that starts the heating and cooling unit. As the temperature moves towards the desired level, the mercury also tips back to the original position until the correct temperature is reached.
There are also two switches that move metal balls on a circuit card. One is connected to the heat/cool mode option, the other is connected to the fan. They are activated when users manually switch the thermostat.
The advances in thermostat technologies have made digital thermostats highly cost effective. The most basic units cost little more than mechanical ones and can have tons of cool features. They are easily identified by a digital read out of the temperature, push-button and/or touch screen features, and use of batteries on the panel. They also work differently and use different components.
Instead of a thermometer, switch, and other components, the digital thermostat uses a thermistor for nearly all its functions. The component is made up of a resistor designed to resist the flow of electricity and slow it down. Thermistors are designed to change this resistance based on the temperature around it. The hotter or higher the temperature climbs, the more resistance present in the thermistor. When a preset temperature is reached, a signal is sent to the cooling or heating system to turn it on until the desired temperature is met, and the resistance in the thermistor drops or rises.
Even basic digital thermostats offer a ton of programming features. This is accomplished by use of a clock which can be programmed by the week, day, hour, etc. Users set the clock and date and can then program different settings for the thermostat. For example, in the colder months the heat can be lowered during night when in bed and not needing as much heat. In hotter months, the temperature can be set higher during the day so as not to cool the home when its occupants are at work, school, etc.
Other Thermostat Types
Non-Programmable Digital Thermostat
Just what they sound like, these are digital thermostats that cannot be programmed to different settings by days or hours. However, for homes that rarely need temperature changes or for those who are confused by programmable thermostats, they can be a viable option. They offer features not found in mechanical thermostats, such as touch screens, digital read outs, and simple interfaces.
Programmable Mechanical Thermostat
Even less common than the above, these are mechanical thermostats that can be programmed. Due to advances in digital technology, not many are in circulation anymore because these mechanical thermostats can be difficult to program.
Similar to a digital thermostat, wireless thermostats (like the Nest unit above) employ the same technology as digital thermostats along with the ability to take the thermostat to any room desired. It employs similar technology as the remote control on your television, and wireless thermostats can even have their own remotes. Users can adjust their wireless thermostat as they like, which will then in turn send a signal to an equipment interface module wired to the heating and cooling system.
If your smart phone can talk, why not your thermostat? These thermostats can announce the time, day, and of course, temperature. They can also respond to voice commands to raise or lower the temperature and other commands. They use a digital signal processor to interpret speech, much like the automated answering services on customer service lines. Senior citizens, those who have trouble pushing buttons, and even the vision impaired can use these thermostats with ease. Another advantage to a talking thermostat is its ability to remind you to change the filers and have it serviced.
Also called telephone thermostats, these can be programmed even if not in the home. This is especially advantageous for those with vacation homes or properties visited only a few times a year. These thermostats can be operated by phoning in and entering a code, automating with a home security or cable system, or even with the aid of a smart phone. There are even Wi-Fi thermostats that utilize Wi-Fi signals to control heating and cooling settings.
Other Components in Thermostats
Even older, mechanical units can employ the use of heat anticipators. Just as their name implies, this component shuts off the heat earlier in anticipation of the time it takes the heated air to reach the thermostat. This device is especially useful in homes with hot spots.
If you live in a home with more than one floor, installing digital thermometers with zone options can save a lot of money. These thermostats can be programmed to set a temperature for each floor. This can be advantageous as heated air tends to rise, which can leave the bottom floor too cold no matter what time of year it is. These thermostats work in heating and cooling systems with dampers in the duct work.
Low/Line Voltage Thermostat
Most thermostats are low voltage thermostats, or they are powered by the home’s electrical system normally at 240 volts.
Line voltage thermostats are more commonly found in smaller units such as space heaters or wall air conditioners. They generally operate at 24 to 50 volts.
Other Important Facts About Thermostat Types
- The cost of replacing a perfectly fine mechanical thermostat with a digital one can be made up and exceeded fairly quickly in homes where the heating and/or cooling is used for long periods of time when no one is home.
- Replacing a thermostat is a fairly easy project for those who like to do it themselves. It involves labeling the wires before removing the old thermostat and then attaching them to the corresponding places in the new one. Be sure to turn the power off to the entire cooling/heating unit when replacing thermostats and consult the owner’s manual on both thermostats.
- A common reason heating and cooling systems stop working is because the batteries in the thermostat (digital only) have run out. Replacing them can often solve the problem.
- Another reason a thermostat can work improperly is because it isn’t level, which throws off the inner components. Use a standard level to make sure this isn’t the case.
- Accumulation of dirt and dust can also cause a thermostat to fail. Consult your owner’s manual for how to remove, clean, and restore your thermostat. Be sure to check for corrosion on wires and contact points.