How Does A Thermostat Work? Everything You Need To Know

Ian Mutuli
Updated on

A thermostat is the most sought feature in a home when the temperature changes. You either head there to change the settings or look at what may have caused the changes. Then, with a button press or a tweak of the dial, you can return the room temperature to its previous setting and enjoy your desired temperature. Well, how does a thermostat work?

A thermostat allows you to control your home's heating and cooling system. Although we only understand how it shifts temperature in different settings, we must understand what makes it do so. This article gives you an in-depth explanation of how a thermostat works. Let's get started!

What Is a Thermostat?

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The word "thermostat" is based on two ancient greek ones "thermo" means heat, and "stat" means standing. It is also related to static, stasis, status quo, or staying the same. So you can tell from its name that a thermostat means something that maintains the same heat levels.

A thermostat is a device found in the walls of most homes. It controls the home's temperature by switching to warm when it gets too cold. Once it reaches your desired temperature, it switches the heating off so you don't overheat.

Types of Thermostats

The two main types of thermostats are:

1. Traditional Analog Temperature Dials

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Traditional analog temperature dials are mechanical thermostats. They use two strips of metal laminated together to form a bimetallic strip in the thermostat sensor. They work through expansion and contraction when the temperature rises or falls.

As the temperature shifts, the thermostat switches the electrical circuit connected to the heating system on and off. They are less accurate than digital thermostats, but most homeowners prefer them since they are affordable, easy to use, and maintain.

2. Modern Digital Thermostats

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Modern digital thermostats are more sensitive and effective than mechanical ones. They read the temperature of the rooms and control the heating to keep it within a degree of your preferred setting.

You can also opt for electromechanical thermostats that offer mechanical and digital features. If you want to regulate your home's temperature, it is good to know the type of thermostat you have and how they transmit information to your boiler. For instance:

  1. You can find digital thermostats that are wireless and battery-operated.
  2. You can get mechanical or digital thermostats connected with wires to your boiler.
  3. You can get the best programmable thermostats that can run the heating at different times of the day if you are absent.

How Thermostats Work

To understand how a thermostat works, we will explain it in terms of heating elements. When you heat most elements, they either expand or become smaller when they cool down. Water is an exception, as it expands when you heat it and also when it freezes.

a) Mechanical Thermostats

Mechanical thermostats work on the thermal expansion idea by switching an electrical circuit on or off. They use bimetallic strips or gas-filled bellows to measure the surrounding temperature and operate the heating mechanism.

1. Bimetallic Strips

Most traditional thermostats use bimetallic strips. These two metals are bolted together to form one strip—the strip functions as a bridge in an electric circuit that connects to your heating system. In most cases, we use the term "the bridge is down" to refer to when the strip carries electrical currents through the circuit, and the heating system is on.

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When the electrical circuit is on, one of the metals expands more than the other to bend the whole strip slightly. Eventually, the heat gets too much that it bends and breaks open the circuit. "The bridge is up" is a term that refers to when the electric current instantly switches off. Finally, the heating cuts out, and the room begins to cool.

The strip cools when the room cools and bends to its original shape. It takes time before it snaps back into the circuit and returns the original flow of electricity to switch the heating on. You can alter the temperature changes by adjusting the temperature dial.

Since the bimetallic strip takes time to expand and contract, you will experience a slow temperature change. It may become irritating depending on how well your house is insulated; it may even take more than an hour for the thermostat to switch to heating your home once it is switched on.

2. Gas-Filled Bellows

As discussed earlier, bimetallic strips take longer to heat up or cool down and do not react quickly to temperature changes. Luckily, there is an alternative design of a thermostat that senses temperature changes faster by using two metal discs with gas-filled bellows in between.

These discs have a large surface area, enabling them to react quickly to heat. They are also corrugated (with ridges) to make them springy and flexible. When the room heats up, the gas in the bellows expands, forcing the discs apart. The inner discs push against a micro switch in the middle of the thermostat, thus turning the electric circuit off.

When the room temperature is lower, the gas in the bellows contracts, forcing the metal discs back together. Then, the inner disc moves away from the micro switch and switches on the electric circuit, turning the heating on.

Corrugated bellow thermostats are also present in other applications, such as older cars, but instead of gas, they are filled with volatile (low boiling) liquids such as dilute alcohol. The chemical inside will depend on the temperature ranges over which they must operate.

3. Wax Thermostats

From what we have discussed, you can deduce that mechanical thermostats are controlled by substances that change their size and shape upon the increase in temperature. So bimetallic thermostats rely on metals expanding when hot while gas bellows work on the expansion of gases.

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However, some thermostats use the change in substances from liquid to gas. These are known as wax thermostats, and you can find them in car engines, home radiator valves, and mixer showers.

They function by using a plug of wax inside a sealed chamber. As temperature increases, the wax melts, expanding and pushing a rod out of the chamber. It then switches the circuit on or off.

It operates the engine cooling system of a car or regulates cold and hot water in a shower to ensure you dont burn while bathing. Wax thermostats are often reliable and longer lasting in controlling extreme temperatures inside a vehicle engine.

4. Thermostatic Radiator Valves

Thermostatic radiator valves regulate the flow of hot water through a radiator to prevent the room from overheating. So let's say the room gets hot; it will trigger a wax thermostat that activates the valve that shuts off the water flow through the radiator until the temperature returns to normal again.

The temperature valves are fitted to central heating radiators using wax thermostats. When these radiators heat up to your desired temperature, the wax valves expand and reduce the water flow through the radiator until the temperature is back to normal.

With room thermostats like these, you can prevent your home from overheating and save energy and money.

Smart Thermostats

Most of us do not spend time at home, but we have a programmer that switches on or off the thermostat in our absence. These programmers are what we call digital thermostats. They include smart thermostats, which you can control via your smartphone. They allow you to regulate temperature wherever you are and help you simultaneously maintain your cool and cash.

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Some also offer machine learning to help it adapt to your daily routine. For example, a digital thermostat help regulate the temperature without wasting energy or money. The smart thermostats learn how to manually alter the temperature at different times of the day, weeks, or even weekends.

They then compare the objective temperature and measure the humidity to establish a reliable program to follow automatically in the future.

Typically digital thermostats allow you to program and operate them remotely using a smartphone app so you can turn the heat up on your way back home.

How To Save Energy While Using A Thermostat

In most homes, thermostats stay on 24/7 to regulate temperature; this may increase your electric bills. Instead, use the following to control your house's room temperature and save energy.

1. Know The Outside Temperature

A thermostat controls the temperature inside a home by battling against the outside temperature. That means if there is a bigger difference between the inside and outside temperature, the system will find it harder to control the temperature and use more energy.

If you want to lower your energy use, you can monitor the outdoor temperature and set your thermostat as close to that number. Doing so will maintain a comfortable atmosphere within your home and save on electricity bills. You can also learn how to replace your thermostat units to help you set them to the right temperature.

2. Keep Calm

If there is an instant increase or decrease in your room's temperature, you might feel the urge to crank your thermostat up or down to bring the temperature to normal faster. However, that is not a good idea as there is only a maximum amount of energy the thermostat can exert at once.

Your home may not cool down or warm up faster simply because you switched the temperature to very high or low. Always keep calm when trying to get your temperature right. Avoid heating or cooling your home, and focus on setting the temperature to your desired degrees on the first attempt.

3. Use Programmable Features

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If you have programmable thermostats, you can take advantage of those features. Try setting your thermostat closer to the outside temperature when you are not in the house. You can use the programmable features on your thermostat to change the temperature once you leave the house and switch it back when you return.

To make things easier, you can use a wifi enable programmable thermostat that allows you remote access using your smartphone or computer. It equips you with precise temperature control and uses intelligent alerts to determine if your home requires heating or cooling automatically.

Apart from the temperature sensor feature, the wifi thermostats also have filter change indicators that figure out when to change pesky filters.

4. Use Energy-Saving Alternatives

If you want to save on energy, you can start cutting back on what you use on your heating and cooling system since there are days when you can't go without air conditioning or heat. In addition, you can try other energy-saving alternatives to help you reduce the number of days your system can run.

In winter, you can use heating blankets or a fireplace to add warmth without switching your thermostat. Likewise, you can use fans in the warmer summer months to help indoor air circulate. When you use the fans alongside your thermostat, you can avoid adjusting the temperatures every time, thus lowering your energy consumption.

5. Take Care of Your HVAC System

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If you maintain your HVAC system properly, you will save a lot of energy. However, suppose your HVAC system has dirty or plugged air filters, or you must schedule service or clean the area around your compressors. In that case, the system will work harder, consuming a lot of electricity.

Be smart in taking care of your HVAC service selection. You can schedule a technician to perform a maintenance service on the system once in a while to ensure it functions optimally and is ready to heat or cool your home.

Scheduling professional checkups can help you find and repair problems before they worsen. In addition, if you maintain a well-functioning HVAC system, you will keep your home comfortable and also save on energy.

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Ian Mutuli

About the author

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.