The human body is designed with complex inner workings that enable us to survive through different types of environments. Outstandingly, it also regulates our internal temperature to adapt to the temperature of our surroundings. Sometimes, however, our bodies aren’t enough to sustain a comfortable temperature. The conditions of our climates can be unpredictable, and the human body cannot keep up at times. That’s where heating, ventilation, and air conditioning (HVAC) systems enter the picture. Although we cannot control the ever-changing temperature of our environment, we can regulate the temperature indoors with HVAC systems. 

HVAC systems provide rooms and vehicles with comfortable temperatures. Simply put, these systems increase the indoor temperature when it’s too cold or decrease the temperature when it’s too hot. To eliminate the need to pry them open and adjust their temperatures, they usually come with convenient components known as thermostats. 

What Is a Thermostat?

When you have an HVAC system in your home or office, you might see a thermostat mounted on the wall. It’s a device that controls and maintains temperature levels. A thermostat is often marked in degrees, or it displays the temperature that an HVAC system produces. 

The word thermostat comes from two Greek Words: thermos, which means “hot,” and statos, which means stationary, like from where the words “static” and “status quo” derive. Like the origin of its name, a thermostat keeps the desired temperature level stationary. However, it doesn’t just function like so. It detects any changes in the room temperature and generates signals to the HVAC system. This way, you can easily set your preferred room temperature, and the thermostat does the job of keeping that temperature constant. When the room gets too cold during the winter months, the thermostat prompts the heater to produce more heat. When the room gets too hot and humid in the summer, this device signals the air conditioning unit to produce cooler air. 

How Does a Thermostat Work?

With this extremely convenient technology, it begs the question of how it works. Basically, thermostats turn HVAC systems on and off, or they control the flow of heat or cooling transfer fluid to maintain the set temperature. Because technology has come a long way since the invention of thermostats, there are numerous kinds of thermostats today, each of which operates differently. Among all of these thermostats, one thing stays the same: they operate on sensors, which read the temperature. 

Mechanical thermostats, in particular, make use of bimetallic strips and gas-filled bellows. These sensors operate on the concept of thermal expansion. This idea focuses on the fact that matter tends to increase in size when it heats up and decrease in size when it cools down.

In heating systems, the bimetallic strip serves as a bridge connecting the dial or thermostat switch and the electrical circuit. When the strip is cold, it stays straight to let electrical currents flow and activate the heating. When the strip gets hot, it expands and bends inward to thwart the flow of electricity.

Since bimetallic strips take a long time to respond to changes in temperature, the mechanical thermostats of heaters come with gas-filled bellows, which are found between two metal discs. These discs are designed to have wide surfaces, which respond rapidly to heat. The gas filling the bellows expands when it’s hot to force the two metal discs apart. Then, one of these discs pushes against an internal switch to turn the heating system off. When the room cools down, the gas-filled bellows contract and the metal disc moves away from the switch to activate the heating system. 

Apart from bimetallic strips and gas-filled bellows, there are other kinds of sensors that thermostats use. For instance, electronic thermostats make use of thermistors or thermally sensitive resistors, resistance temperature detectors, thermocouples, and other semiconductor devices. Unlike bimetallic strips, which operate mechanically, the sensors of electronic thermostats run on electronic heat-sensing elements and circuits.

Parts of a Thermostat

Understanding the parts of a thermostat can make it easier for users to purchase replacement parts if need be. Aside from sensors, a thermostat is composed of a base, a cover, and a subbase. The base is where the internal wires of a thermostat sit. A thermostat’s wires are arranged according to the type of switch, type of anticipator, fan and system switches, type of voltage, and the number of field wires. 

The types of thermostat switches include single-pole single-throw, single-pole double-throw, double-pole single-throw, snap-action, or mercury bulb. The types of anticipators are based on the HVAC unit type, whether it is used for heating or cooling. Lastly, thermostats run on low voltage, line voltage, or millivolt circuit.

Secured to a thermostat’s base is the cover. Its main function is to protect all of the wires connected to the base against dust and other contaminants. The thermostat cover consists of the levers for setting the temperature and for turning the HVAC system on and off. It also displays the temperature.

The subbase is more of an extra component rather than an essential part of the thermostat. It holds additional thermostat switches for fans and other functions. 

There are also accessories that users can buy for thermostats. The most common thermostat accessory is a thermostat guard, which provides the device with additional protection from damage. Protecting thermostats with guards can be particularly useful in hazard-filled areas, such as warehouses and factories. Some thermostat guards also come with locks to prevent tampering. 

Signs of a Broken Thermostat

When a thermostat breaks or stops working, the room feels extremely uncomfortable to stay in, especially during freezing winters and hellish summers. However, before calling a technician to repair the thermostat, make sure that the thermostat isn’t the problem. Look out for these common signs of a broken thermostat.

1. The HVAC System Won’t Turn On

If switching on the thermostat won’t activate the HVAC system, the thermostat’s wiring must be defective. This issue usually calls for a professional to repair the thermostat. Before doing so, check for blown fuses, short circuits, or dead batteries. Also, check if there’s dust buildup inside the thermostat.

2. The HVAC System Won't Turn Off

Another symptom of a wiring defect is that the HVAC unit won’t turn off. The heater unceasingly produces hot air, or the air conditioning unit continues to produce cool air even when the thermostat is switched off.  Defective wiring or a miscalibrated thermostat might cause this issue. 

3. Unable to Detect the Room Temperature

Feeling colder or hotter than the temperature you’ve set on your thermostat? The problem might be your thermostat’s inability to read the temperature. The location of the thermostat can be the cause, so check first if the thermostat is placed directly under sunlight or near open windows. If that’s not the case, confirm that your thermostat is broken by placing a thermometer next to it. Wait for at least 15 minutes for the thermometer to stabilize. If it doesn’t match the thermostat’s temperature, it’s time for a professional to step in. 

4. Unresponsive Thermostat

A thermostat can be considered unresponsive if it continues to display a blank screen after turning it on. An unresponsive thermostat also fails to change the room temperature even after it’s adjusted. For this issue, see if it needs a change of batteries. If dead batteries aren’t the problem, then the thermostat needs to be repaired or replaced. 

Types of Thermostats

If you’re about to buy a thermostat for your new HVAC unit or if you need to have your old one replaced, there are different types of thermostats from which you can choose. They offer various features to be compatible with your HVAC unit and to suit your preferences. 

1. Mechanical Thermostat

The mechanical thermostat is the most common and basic type of thermostat there is. As previously mentioned, it makes use of bimetallic strips to sense temperature changes. To activate a mechanical thermostat, it has to be manually switched on. Likewise, it has to be manually switched off or switched from heating to cooling and vice versa. Most mechanical thermostats feature dials, which allow users to adjust the room temperature. When setting this thermostat at a fixed temperature, the temperature will stay the same unless it is shut off. Although this type of thermostat offers traditional controls, it is still widely used today because it is the least expensive option of thermostats. 

2. Digital Non-Programmable Thermostat

Much like a mechanical thermostat, a digital non-programmable thermostat has to be manually controlled whenever it has to be turned on and off or adjusted. What makes this thermostat different from a mechanical one is that it makes use of thermistors or other semiconductor devices instead of bimetallic strips. A digital thermostat also features a digital display, which shows the temperature readout and settings. This display makes it easy for users to read the temperature, control their HVAC system, and adjust the thermostat’s settings. Compared to more modern thermostats, however, a non-programmable thermostat has to be manually powered off. 

3. Programmable Thermostat

Convenient and efficient, a programmable thermostat lets its users set temperatures at different time schedules throughout the week. This thermostat eliminates the need for manual adjustment since it automatically changes the temperature based on the set schedule.

For instance, during summer, users can set this thermostat at a higher temperature when there’s no one at home. It can be programmed to activate its air conditioning feature automatically right before everyone goes home. 

There are programmable thermostats that allow users one program per week, and there are others that can shift to different settings from day to day. With this type of thermostat and its automatic scheduling feature, you can save on electric bills since it can automatically shut off on schedule. 

4. Wireless Thermostat

Wireless thermostats offer convenience when it comes to controlling HVAC systems. Users can easily access their devices’ settings from any part of the room. Since these thermostats transmit signals to HVAC systems through wireless technology, users can control their devices remotely. Wireless thermostats also make it easy for users to upgrade their HVAC units without the need to run wires. 

There are also wireless thermostats that can connect to mobile devices via Wi-Fi and Bluetooth. They allow users to control their HVAC units with the use of their phones, tablets, and computers. This feature can help save energy and keep the temperature constant throughout the office or house. 

5. Smart Thermostat

With the continuous breakthroughs in technology, devices such as thermostats have become smarter and more convenient. Like programmable thermostats, smart thermostats feature temperature scheduling so that users can set different temperatures throughout the day or week. What makes this type of thermostat different is that users can control it through mobile apps anywhere, anytime. 

A smart thermostat also makes use of a technology that learns the user’s daily routine or schedule. For instance, it determines the time when there’s no one at home or in the office. This feature allows the thermostat to learn your preferences whenever you use it. The smart thermostat also creates programs by itself based on those preferences, so it doesn’t require users to set temperature schedules.  

Because of its complex yet convenient features, it’s more expensive than other types of thermostats. However, a smart thermostat can be a good investment since it can help save on utility bills, especially in the long run. It’s also convenient for busy users in case they forget to turn off their HVAC systems before they leave their homes.

Choosing a Thermostat

Before selecting the right thermostat for your home or office, you have to check what types of thermostats are compatible with your HVAC unit. While most thermostats nowadays are compatible with HVAC systems, some smart thermostats and other types of thermostats do not support all HVAC models. Also, when you own two separate units for heating and cooling, each of these systems requires a separate thermostat. 

After checking the compatibility of thermostats and your existing HVAC unit, you should determine your needs and preferences when it comes to comfort conditioning. If you’re at home often and you need a more affordable thermostat, a mechanical thermostat or a digital non-programmable thermostat is enough. To save more energy, a programmable thermostat can automatically turn off on schedule. To control your device from any part of the room, use a wireless thermostat. If you’re looking for the most convenient way to control your HVAC unit, a smart thermostat might be the best one for you. 

With the right thermostat, you can simply sit back, relax, and enjoy the comfortable heat or coolness in the room. It’s always best to choose a thermostat from a brand that’s known for its quality products. Engineer Warehouse has selected thermostats from only the best brands, and these thermostats will surely make any room feel more comfortable and habitable. 

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Diet Salazar is a researcher and technical writer of information-packed articles for various industries, including the AEC industry. She spends her free time learning about small building projects and new design trends.