How Does A Furnace Thermostat Work? A Comprehensive Guide

Furnace Thermostats

To help you understand thermostats with its types and features, let me introduce you to the section “Understanding Thermostats”. In this section, we will talk about the different types of thermostats and their features. We will start with the definition of thermostat, followed by the purpose it serves and its importance in HVAC systems.

Image of a furnace thermostat of a furnace

Definition of Thermostat

It’s essential to know about thermostats. They’re devices that can change the temperature of a room or building automatically. They save us money, and make our homes comfy.

There are different models with varying features. For instance, some have multiple daily schedules. Or, voice command capabilities. Smart thermostats can even be controlled remotely with apps or hubs. It pays to know the details and pick the one that’s right for us.

If we don’t update an old thermostat, energy bills will rise. This means missing out on savings. Upgrading sooner can prevent costly issues. Plus, save us on utility bills.

Purpose of a Thermostat

Thermostats have a purpose. It is controlling temperatures in our homes. Monitoring and regulating heating and cooling systems is just the beginning. Modern thermostats boast advanced tech features to provide energy efficiency, home automation and cost-saving.

Touchscreens, remote access via smartphones or computers, voice commands and AI are all included. Digital assistants can set temps but also detect changes beyond normal schedules to adjust accordingly. These devices can even predict the home’s temperature needs before occupants realise it.

Thermostats have been around since the 17th century. Back then it was referred to as a “temperature regulating device”. In 1883, American inventor Albert Butz designed the first modern thermostat, the “Butz Thermo-Electric Regulator”. That could automatically adjust temperature/pressure in a steam room, no human involved. 

Since then, thermostats have continued to evolve with more advanced features giving us more control over our environments.

A thermostat is essential for an HVAC system, it’s like a conductor for an orchestra.

Importance of a Thermostat in HVAC Systems

Thermostats appear small and insignificant in HVAC systems. But their role is critical like to regulate temperature and energy usage. The thermostat senses the current temperature and signals the heating or cooling system to turn on or off until it reaches the desired temp.

Plus, thermostats help you save energy costs. Programmable ones have customized schedules, so the system doesn’t run when no one is home.

Did you know adjusting your thermostat by one degree can save up to 1% on your energy bill? The U.S. Department of Energy states, lower your thermostat by 7-10 degrees for 8 hours a day to save 10% annually on heating and cooling costs.

Whether you like manual or programmable thermostats, their aim is the same to keep you from freezing or sweating.

Types of Furnace Thermostats

To understand the different types of thermostats for your HVAC system, let me guide you through the solutions. In this segment, we will discuss two types of thermostats, Mechanical Thermostats and Electronic Thermostats. Each of them has a unique way of maintaining the comfortable temperature in your home, and we will explore them briefly.

Mechanical Thermostats

Mechanical thermostats are found in older homes and business spaces. They use a metal strip duo with different expansion rates. As the temperature changes, the strips expand or contract, turning the heating or cooling system on or off. No electricity is needed for them to work, so they’re reliable during power outages. However, they may not be as accurate as other thermostats, causing temperature swings.

To improve accuracy, clean and calibrate them regularly. Dirt and dust buildup can affect performance. Or, install a programmable thermostat to work with the mechanical one for more precise temperature control.

By understanding mechanical thermostats and following these suggestions, homeowners and building managers can get consistent and reliable heating and cooling, while keeping a vintage feel.

Bimetallic Strip Thermostats

Bimetallic strip thermostats are an essential part of temperature control systems. They use two metals strips, one with a higher thermal expansion coefficient than the other. When heated or cooled, the strips expand or contract at different rates, causing them to bend and move apart. This movement activates a switch that controls the heating or cooling system.


  • Low cost
  • Easy maintenance
  • Wide range of applications


  • Slow response time
  • Inaccurate temperature control at extreme temperatures

These thermostats are a unique option for both heating and cooling applications over a wide temperature range. However, they have slower response times than other thermostats.

The history of bimetallic strip thermostats goes back to the early 1800s when French physicist Jean Charles Athanase Peltier discovered the thermoelectric effect. Later, in the mid-1920s, Honeywell introduced the first commercial version of the device, which has been widely used ever since.

Different types of thermostats offer various advantages and disadvantages that make them suited for different applications. By understanding their features and capabilities, you can pick the right thermostat for your needs. Expansion bellows thermostats offer your heating system a chance to inhale and exhale, like a yoga class for your house.

Expansion Bellows Thermostats

Expansion bellows thermostats are a type of thermostat that uses a flexible metal bellows to detect temperature changes. These thermostats are popular in industrial applications as they can manage high pressures and temperatures with precision.

Let’s have a look at the features of this type of thermostat:

  • Operation range: -200° C to 600° C
  • Pressure range: Up to 1000 PSI
  • Bulb diameter: 0.5″ – 2.5″
  • Sensitivity: +/- 1% F.S.D
  • Contact type: Single pole double throw or single pole single throw.

What’s special about them is that they have an all-metal design, making them suitable for even the toughest environments.

If you’re going to use an expansion bellows thermostat, keep these tips in mind:

  • Install and calibrate for best performance.
  • Regularly check for physical damage or leaks.
  • Use insulation and safety shields when working with high temperatures.

By following these tips, you can ensure your thermostat’s accuracy and longevity.

Mercury Switch Thermostats

Mercury switch thermostats are an old-school type of thermostat. They use a small glass capsule with mercury inside. It expands and contracts based on the temperature changes. This controls the heating and cooling system. 

Here’s more info:

Column 1Column 2Column 3
What it isHow it worksPros & Cons
A type of thermostat using mercuryMercury expands & contracts in relation to temp changes, controlling the heating/cooling systemPros: reliable & accurate. Cons: harmful if broken or not disposed properly.

Exposure to mercury can cause health issues. That’s why these thermostats have been phased out. But, they still exist in many older homes.

I recently read about a guy who broke a mercury switch thermostat during renovations. Unfortunately, he didn’t know the risks so he cleaned up the mess without proper gear. The result? Mercury poisoning and a hospital visit. This incident shows how important it is to handle and dispose of these devices properly.

Electronic Thermostats

Electronic thermostats use electronic sensors to precisely regulate room temperature. They’re programmable, too, allowing you to set up heating and cooling times. Plus, they can link with home automation systems, so you can control them remotely with a mobile app or smart device.

To maximize your savings, you can program energy-saving settings. This’ll reduce energy consumption when you’re not home or sleeping, saving money on utility bills and reducing your environmental impact.

And don’t forget that Electronic Thermometer Coil Thermostats make things hot and heavy.

Thermometer Coil Thermostats

Thermometer coil thermostats are a popular type of thermostat. They use coiled wire to sense temperature changes and regulate the heating or cooling system. 

Advantages of thermometer coil thermostats include:

  • No power needed to operate, perfect for areas without electricity or with frequent power outages.
  • Easy installation and maintenance. No batteries or complex wiring needed.

When selecting a thermometer coil thermostat, consider factors like price range and compatibility with your existing heating or cooling system. This will help you choose a high-quality thermostat that meets all your needs.

Digital Thermostats

Digital thermostats have revolutionized the heating and cooling industry with their advanced features and efficiency.

Precise temperature control, programmable settings, and remote access through smart devices are all benefits of digital thermostats.

Below is a table showing different types of digital thermostats and their features:

Thermostat TypeFeatures
ProgrammableTemperature changes based on time of day
Smart/Wi-Fi enabledControl remotely via smartphone app
LearningLearns and adjusts to temperature preferences
TouchscreenEasy programming and adjustments

Plus, some digital thermostats can be integrated with other smart home devices like Amazon Alexa or Google Assistant.

Investing in a digital thermostat has many advantages. It can save money on energy bills by optimizing the temperature. Plus, it can ensure consistent temperatures for comfort.

Don’t miss out. Upgrade your heating and cooling system now. Enjoy a more comfortable and cost-effective environment with a digital thermostat. If only it could also turn down the heat on my ex’s angry texts.

Smart Thermostats

Smart thermostats are the latest in home technology that provide efficient heating and cooling for homes. These come with innovative features that allow remote control from your smartphone, tablet or computer.

They’re also smart enough to learn your temperature preferences. Plus, you can set schedules tailored to your needs. Real-time energy reports, historic usage tracking and more are available on the easy-to-use interface.

For those who like a hands-free experience, some models offer voice control compatibility with virtual assistants like Amazon Alexa and Google Home. Installation is simple, with most models providing a drill-free setup.

Integrating with other smart home devices, like locks and security systems, lets it all work together towards one common goal. Governments have even offered rebate programs to encourage folks to make the switch.

How a Furnace Thermostat Works

To understand how a thermostat works with electrical circuit, temperature dial/setting, heat anticipator, mode switch, and mechanical components, think of it as something that helps you control the temperature of your home or office in the most convenient way possible. 

By adjusting the temperature settings on the thermostat, you can turn the heating or cooling system on or off, change the mode of the HVAC system, and select the proper ambient temperature for a certain area or room. The electrical circuit and mechanical components play a crucial role in making sure that the thermostat can take the temperature changes inside the house and send the right signals to the HVAC system.

Electrical Circuit

A thermostat’s electrical circuit is the path through which electricity flows, providing power. It consists of parts like a power source, wiring, and switches. The thermostat senses temperature changes and activates the relevant parts to control the heating or cooling system.

Inside, a bimetallic strip bends and causes an electrical switch to activate the system. A triac may also be used with a heating element, like in an electric furnace.

Checking connections, fuses, and wires is important for safety and efficiency. Always refer to manufacturer instructions when troubleshooting. Otherwise, it can cause damage or injury.

Temperature Dial/Setting

The Temperature Dial/Setting on a thermostat allows you to control the HVAC system in your home. To adjust, turn clockwise to increase temperature and the HVAC system will run longer. Turn counterclockwise to decrease temperature and the HVAC system will run shorter.

It may take a while for your home to match the temperature you set. Some models are programmable, meaning they can adjust temperatures automatically based on time or day.

According to the US Department of Energy, turning your thermostat back 7-10 degrees Fahrenheit for 8 hours a day can save 10% on annual heating and cooling costs. Even your thermostat knows to anticipate the heat better than your ex!

Heat Anticipator

Thermostats are essential for home temperature control. Inside, there’s a small current regulator called the heat anticipator. It helps the furnace turn on and off at the right time and keeps the temperature in check.

To keep it running smoothly, calibrate it during installation and maintenance. Don’t forget to keep it clean too. Gently use sandpaper or an emery cloth on the contact surfaces and blow away any debris. Now you can enjoy reliable temperature control all year round.

Mode Switch

The Mode Switch is the hub of a thermostat’s functioning. It controls and maintains the temperature mode.

Mode Switch also caters to a range of heating and cooling settings with a fan autoplayer that circulates air flow. This makes it easier than ever to maintain comfort.

Nowadays, thermostats have become digital. They can support multiple zones, they learn user behavior and enhance energy efficiency. And these smart thermostats integrate with smart home systems too.

So, for optimal results and usage from your thermostat system, make sure your model is using this state-of-the-art technology. It saves you bundles over time while maximizing comfort. Why rely on your instincts to adjust the heat when a thermostat can do it for you?

Mechanical Components

Mechanical components are essential for thermostats. These parts include a bimetallic strip, mercury switch, and thermostat dial.

The bimetallic strip changes size depending on temperature, making it bend and break electricity controlling cooling or heating. Mercury switches work similarly, but use mercury instead of a bimetallic strip. The thermostat dial lets users adjust the desired temperature.

Newer thermostats use electronic components rather than mechanical parts, and provide more accurate temperature control and energy efficiency. Even so, accurate sensing of the temperature is important for smooth operation.

Recently, a friend told me about installing a smart thermostat in his home. He can control the heating and cooling from anywhere using his phone and also get detailed info on energy use, so he can reduce bills without sacrificing comfort. Thermostats remain a reliable way to manage indoor climate due to tech advancements. To sum it up, bimetallic strips are like two-faced politicians, they bend whichever way the temperature goes.

Bimetallic Strips/Metals

Bimetallic Strips, or Metals, are important parts of thermostats. They heat up and bend, cool down and straighten, making an electrical signal to the heating or cooling system. Let’s analyze how they work.

The table below shows the two metals that make up a bimetallic strip, and their function:

Metal AMetal BFunction
CopperInvar (Nickel)Cooling

Both metals expand differently when heated. This makes the strip change shape, which is used to turn on/off a switch or valve in the thermostat.

Although each strip varies slightly in design and components, they all use the same concept, two metals with different thermal expansion coefficients.

It all began with English carpenter John Harrison. In 1832, he invented the bimetallic strip by joining two metals with different thermal expansion. When heated/cooled, one side expands faster than the other, making the strip curl. Nowadays, these strips are used everywhere from thermostats to hair dryers.

Glass Vial/Mercury

A glass vial and mercury are two components of a thermostat. The glass vial holds the mercury which changes size to control the temperature. 

Here’s a summary of the properties of the Glass Vial/Mercury type of thermostat:

  • Property: Mercury.
  • Enclosure: Glass bulb.
  • Sensitivity: High.
  • Accuracy: Good.
  • Response Time: 5-10 mins.
  • Application: Domestic & commercial heating systems.

Be aware, mercury can be bad for humans. So, other types of thermostats have been invented.
If you want to change your Glass Vial/Mercury thermostat, make sure it fits your needs. 

Consider compatibility with your heating system, accuracy level, and response time. Ask an HVAC pro for help in selecting the right model.

Metal Coil/Wiper

The metal coil and wiper are essential for a thermostat’s performance. If the temperature changes, the metal coil expands or contracts. This movement of the coil causes the wiper to move

This then changes the position of the contact point. When the contact point changes, it activates or deactivates an electrical circuit. This action turns on or off the cooling or heating.

Metal Coil: Expands/Contracts with Temperature Changes
Wiper: Moves to Change Position of Contact Point
Contact Point: Triggers Electrical Circuit On/Off

It is important to keep these components clean to preserve accuracy and efficiency. Cleaning and maintenance help them stay in good condition.

You can also improve energy efficiency by replacing old thermostats with programmable ones. This ensures your home has a comfortable temperature while keeping energy bills low. Amazing how a metal coil can control our climate.

Expansion Bellows/Metal Discs

Thermostats are made up of different components that work together to regulate temperature. A significant piece is the Expansion Bellows/Metal Discs. They are indispensable in sensing and controlling temperature changes.

The Expansion Bellows and Metal Discs serve the purpose of detecting ambient temperature variations. Metal Discs are made from a bimetallic material, having one side that contracts more than the other when heated. It causes stress in the metal, making it bend or expand, which gets picked up by a sensor in the thermostat. 

The expansion bellows also use a similar mechanism, but with accordion-like folds instead of a pressurized disc-shaped component, completely eradicating hysterises.

ComponentMaterial CompositionWorking Mechanism
Expansion BellowsCopper, Brass (diameter usually less than 1” diameter) or Steel for larger pipesA sealed housing that expands or contracts due to thermal stress created by temperature change
Metal Discs/Bimetallic StripsMetals such as Copper, Brass, Iron, Nickel, or Aluminium can be bi-metalled together creating a uniform expansion profileMade with two different types of metals layered together like sandwich filling. As heat increases one type expands more, causing bending

What makes them special is their accuracy in measuring temperature fluctuations across various environments like homes, businesses, and industrial settings.

You will be amazed to know that these are not new inventions. Expansion bellows have been used since Roman times in heating systems to control water flow. 

Thermostat and HVAC Systems

To understand how your home’s heating and cooling system works, you need to know how the thermostat operates. The thermostat is the control center of your HVAC system, and it helps regulate temperature, energy usage, and comfort levels in your living space. 

Heating and Cooling Systems

Heating and cooling systems are vital for controlling inside temperatures. HVAC (heating, ventilation, and air conditioning) systems use a mix of heating, cooling, and ventilation techniques to keep you comfortable.

Furnaces warm air and disperse it through ducts using gas, oil, or electricity. Air conditioners cool the air by transferring heat outside. Heat pumps both warm and cool air with refrigerant. Lastly, thermostats sense the temperature and adjust the HVAC system for efficiency.

Traditionally, heating and cooling is powered by fuels like gas and oil, but newer options offer energy-efficient alternatives such as geothermal or solar power. Maintenance is key to keeping HVAC systems in good condition.

System Zoning

No need for someone else to control your fan, a thermostat can do it better.  It’s the perfect way to stay cool.

Control of the Fan

Controlling the fan is key to keeping HVAC systems at optimal temperatures and airflow. Here are four tips for managing it:

  1. Programmable thermostats can adjust fan run-time settings based on occupancy and weather. This prevents energy waste while keeping air cycling even when heating or cooling isn’t required.
  2. Variable speed fans save energy and reduce noise when running at low speeds.
  3. Zoning systems offer separate controls for each area served by a common HVAC, so you can customize comfort.
  4. Fan only switches or controls activate the fan without triggering heating or cooling cycles, so air keeps circulating for better IAQ.

Controlling the fan well cuts energy costs, boosts IAQ, and increases comfort levels. Smart thermostats with built-in sensors recognize occupancy and adjust HVAC settings automatically. High-efficiency filters capture pollutants and extend service life.

These strategies lead to more efficient and effective HVAC management. Plus, they lower utility bills and improve IAQ. To maintain your thermostat, regular upkeep and a good support system are essential.

Tips and Guide for Using and Maintaining Thermostats

To ensure that your thermostat works efficiently with your heating and cooling system, you must take care of it regularly. Therefore, in order to help you maintain your thermostat, this guide will provide you with tips and best practices. 

Firstly, we’ll discuss how to set the right temperature. Following that, we’ll give you tips on how to effectively switch between heat and cooling modes. Then, we’ll explain how you can optimize energy usage and save money on your energy bill. 

Finally, we’ll share some tips on how to maintain and clean your thermostat to ensure it lasts longer and operates optimally.

Setting the Right Temperature

When aiming for the perfect temperature, you want to be comfy and conserve energy. 

Here’s what to do:

  1. Find Ideal Temp: 68 – 72 degrees Fahrenheit is ideal for most homes.
  2. Time of Day Matters: Change the thermostat up or down when people sleep or wake.
  3. Seasonal Settings: Use seasonal settings when out of town to use less energy.
  4. Make Adjustments Gradually: To avoid higher energy costs, adjust slowly.
  5. Utilize Fan Settings: Circulate air and distribute heat or cold evenly.
  6. Upgrade Your Thermostat: Consider a programmable model with zoning features.

Additionally, check filters regularly and keep them clean. This will help your HVAC system run optimally. Have a technician come in every few years for routine maintenance and catch any issues before they become worse.

Set the right thermostat temperature, practice some habits, and you’ll save money while staying warm and cozy. Upgrade to a smart thermostat and never look back.

Switching Tips

Clean your thermostat. Use a soft cloth to wipe away any dust. This will help keep it functioning and extend its life. The US Environmental Protection Agency (EPA) says that correctly setting and maintaining your thermostat can save you up to $180 per year on energy costs. 

Optimizing Energy Usage

Maximizing energy use with your thermostat is key. Lowering it just one or two degrees can save you up to 10% each year. 

In winter, set it to 68 Fahrenheit, in summer, 78. Programmable thermostats can save cash too. Just set schedules to fit your lifestyle and turn off when you’re away.

Maintenance is essential for optimizing energy. Clean or change air filters to reduce strain on HVAC systems. Keep thermostats away from heat-emitting items like lamps and electronics. Plus, avoid direct sunlight.

Kelly’s experience proves how much you can save. She has a large house with many rooms. After adding multiple smart thermostats, she saved $500 a year. Comfort, energy savings, all seasons. Smart or programmable thermostats, plus cleaning, helps optimize energy use.

Maintaining and Cleaning Thermostats

Caring for your thermostat is key for efficient long-term functioning. Maintenance reduces future breakdowns which can be expensive to repair. 

Here are some tips:

  1. Shut off power and remove cover gently.
  2. Use a soft brush or compressed air to get rid of dust and debris in the inner components.
  3. Ensure all screws and wires are secure before putting the cover back on.
  4. Test the temperature readings after cleaning.

Schedule a professional inspection at least once a year. This way, faults can be detected early before they become worse. After cleaning, make sure it is level. Imprecise positioning will cause issues with temperature regulation. Check that it gets direct airflow with no obstructions.

Burning out of thermostats was a problem in the 19th century due to bi-metallic materials. This caused sync problems between room temps and heating systems. Contacts would fail, wasting electric without heating or cooling. Knowing how a furnace thermostat works helps to avoid using it as a toy.


Grasping the functioning of a furnace thermostat is essential for keeping a steady temperature in your home. They work with changes in heat and are beneficial for both heating and cooling systems. There are various types, like mechanical thermostats that use metal strips or bimetallic strips, electronic ones with extra features, and smart thermostats that can be managed from a phone. Bimetallic strip thermostats are the most popular nowadays. As temperatures fluctuate, they expand or contract. This causes a circuit to join with a switch, which then switches on the heater when the atmosphere is below the desired setting. The metal’s thermal expansion bends the strip, breaking contact with one terminal while joining another terminal connected to electrical power. This activates a gas valve, controlling the amount of fuel that passes through to heat an area. Electromechanical thermostats also exist. They comprise of bellows made up of two metal discs filled with mercury vial (glass case). These pliable discs contract when cool and expand when warm, making mercury move onto one side of the vial and break off another side’s electrical circuit card connected to electricity running through switches that control whether it’s getting cooler or warmer.