Although HVAC thermostats usually have a lifespan of 10 to 12 years, there will come a time when your old thermostat will not be able to function anymore, and you’ll have to replace it. Or perhaps you want to replace your thermostat to upgrade your HVAC system. Whatever the reason, you most probably wonder whether the replacement of a thermostat is a DIY job and what aspects need to be considered before and during the replacement procedure.    

A DIY-er with good knowledge about electric wiring and his home’s HVAC system might be able to replace most thermostats. Smart thermostats, however, are usually only replaced by a qualified professional. To buy and replace a thermostat, a homeowner has to consider many aspects, including compatibility as the most important factor. 

In this article, I’ll provide answers to many of the common questions homeowners usually have when they want to replace a thermostat. I believe that when you’ve read the article, you’ll have a good idea of not only what to consider before you buy a thermostat but also whether the replacement should be done by yourself or rather by an HVAC professional.

Photo of a person installing a thermostat

Basic tools needed 

If you are a DIY-er you’ll at least need the following tools to replace your thermostat: 

  • Screwdriver
  • Approved voltage tester
  • Pencil
  • Drill
  • Mini spirit level
  • Some wiring (for when needed)

Before you start the replacement procedure yourself, I recommend you reading this section of the article; Can I replace a thermostat myself? If you then decide to proceed, follow these steps:

How To Replace A Thermostat: Detailed Steps

Step 1: Purchase the right thermostat

Ensure that you purchase a thermostat that is compatible with your HVAC system. Usually, the information on the thermostat’s packaging indicates what types of systems the thermostat can be used for. 

If you want more detail and tips on how to get the right and best thermostat for your HVAC system, refer to Question 2 in our “Technical Guide and FAQs.”

Step 2: Turn off the power

For safety reasons, turn off the power to the thermostat, air conditioning furnace, and other HVAC devices. The safest way to turn the power off is to flip the relevant circuit breakers in your breaker box to the “Off” position. Sometimes all the HVAC devices use only one circuit breaker, but usually, the circuit breakers are labeled, and you can easily determine which ones you have to turn off. If the circuit breakers are not labeled, it is recommended that you turn all the circuit breakers off.  

For more information on the possible problems you can encounter when the power is not switched off before replacing your thermostat, refer to Question 3 in our “Technical Guide and FAQs.” 

Step 3: Remove the current thermostat from the wall

Thermostats usually slide upward from where they are attached to the wall. After you’ve removed the thermostat and there is a baseplate, loosen the screws and remove the plate from the wall. If your current thermostat has a base and sub-base, you must remove the entire thermostat. Only the exposed wires and the bare wall must be left. 

Step 4: Make notes of the existing wire connections

Before you remove the wiring from the current thermostat, put a piece of tape on each wire and write the letter of the connection on the thermostat on the tape. If, for example, the wire is in the thermostat’s receptor marked “B,” write “B” on the label. This will enable you to connect the wires correctly to the new thermostat. Also, label unconnected wires as “Not connected.”

It can also be helpful later if you take a photo of the wiring before you disconnect the wires. 

Step 5: Disconnect wires from the recent thermostat

For most thermostats, you’ll need a small screwdriver to untighten the screws that are holding the wires in place on the thermostat. To ensure that the loosened wires don’t fall back into the wall, tie the wires together or tape them to the wall.

Step 6: Install the new thermostat’s wall plate

Mark on the wall where the screws for the new thermostat’s wall plate must be drilled. Drill the holes, and screw the replacement wall plate into its position on the wall. If necessary, use a mini spirit level to ensure that it is correctly placed.

Step 7: Connect the wires

Use the labels that you’ve put on the wires when you’ve disconnected them from the old thermostat to connect the wires correctly to the new thermostat.  The thermostat’s terminals will be marked with letters, and if you’ve labeled the wires clearly, the connection process is quite easy. 

Depending on the brand and model of the thermostat, you’ll either have to secure the connections by tightening the screws on the receptors, or you just have to push the wire into the receptor to lock it in place. 

Step 8: Insert the batteries and attach the new thermostat to the wall

Most thermostats need AA or AAA batteries to work. Insert the batteries correctly and replace all wires back into the wall. Then place the thermostat flush against the wall. Put it slightly above the wall plate and slide it down to catch the grooves on the wall plate.

Step 9: Turn the power on

Put the circuit breakers on again so that the thermostat and other HVAC devices receive power again. 

Step 10: Configure your new thermostat

Every thermostat is different when it comes to configuration, so just follow the steps in the thermostat’s user manual. When you’ve done the configuring, you’ve successfully installed your new thermostat!

Video of Installing a thermostat

More questions

Many of your questions regarding the replacement of your thermostat will be answered further on in this article. After you’ve read it and decided to replace the thermostat yourself, open the new thermostat’s box and follow the manufacturer’s instructions which should be inside the box.  

Why is it not always as easy as it looks?

There is no “fit-all” replacement kit or manual when you have to replace your thermostat. Although it is a logical process, each thermostat brand and model has its own “special” aspects to take into account when replacing thermostats. 

Manual, programmable and smart thermostats all have different ways to be replaced or to be the replacement for an old thermostat. Almost all thermostat manufacturers, for instance, recommend that only qualified and registered electricians or HVAC professionals replace smart thermostats. 

This is due to the complex voltage changes that have to be done and other compatibility issues that have to be sorted out by a professional. The whole smart thermostat process is too complex and dangerous for a DIY-er to handle. 

Can I replace a thermostat myself?

When you have to replace the HVAC thermostat in your home, one of the first questions you usually ask yourself is whether you should do the replacement yourself or should you get an HVAC expert or electrician to do it for you.

In short, the answer is yes you can do it yourself if you have some expertise, but there are many reasons as well, why it is not a good idea to replace the thermostat yourself. 

When can a DIY-er do it?  

If you are an experienced DIY-er you will most probably be able to do the replacement yourself. But you should not try to do it on your own if you don’t have basic electrical knowledge and have a good idea of how the thermostat and your whole HVAC system work.  

If you decide to install the thermostat yourself, make sure that you re-connect the wires that have been connected to your current thermostat correctly to the new one.  Also, ensure that if you’re replacing a conventional thermostat that has a mercury switch, you don’t break the toxic substance tube.

Reasons why it is perhaps better to get an expert to replace the thermostat

The following are some of the dangers you can encounter and the costly damage you can cause by installing a thermostat incorrectly: 

  • You can get an electric shock if you unknowingly have left on some power supply to the thermostat or other HVAC devices. 
  • You might blow a circuit breaker if you connect the wires incorrectly. 
  • The thermostat, and even the air conditioner or furnace unit can get damaged if you handle the thermostat incorrectly.
  • Advanced HVAC systems often require more detailed knowledge from the installer than is normally needed. 
  • You can unknowingly send too much current through the thermostat and cause it to fail.
  • Thermostat manufacturers could decide not to honor the thermostat’s warranty if the installation hasn’t been done by an HVAC professional.

How Much Does It Cost to Replace a Thermostat with an Electrician?

Usually, it takes about 1 to 2 hours for an electrician to install a thermostat. And electricians charge anything from $60 to $150 per hour. In other words, it will cost you between $120 and $300 if you use the services of an electrician to replace your thermostat. Currently, the average cost of installing a thermostat in the United States is $175.

Thus, installing a thermostat yourself can save you labor costs. But as indicated elsewhere in this article, if you do the installation yourself, the thermostat manufacturer might decide not to honor the warranty if you encounter problems. Then you’ll have to pay for all expenses regarding the rectification of the problem.  

There is also always the risk that you can unknowingly damage your thermostat when installing it and then you have the extra expense of purchasing another thermostat (or even an air conditioner or furnace if one of them has been damaged). 

Can I replace a thermostat with any thermostat?

Nowadays, many replacement thermostats are compatible with common HVAC systems. But because of the uniqueness of some systems, it is possible that not all thermostats are compatible with your HVAC system. Especially, smart thermostats might have problems synching with your existing HVAC system.

Some thermostats also only work with furnaces and air conditioners, while others are designed for heat pumps and multiple-stage systems.

How do I know what thermostat to buy?

You may now wonder what replacement thermostat you have to buy. The easiest will be to buy a thermostat identical to the current one in your HVAC system. But your current thermostat might be as old as 10 or 12 years and you cannot find exactly the same thermostat anymore.  Or perhaps you want to upgrade your system while you have to replace your thermostat in any case. 

To assist you to make the right choice we recommend that you follow the next steps: 

 Step 1: Decide on the type of thermostat you need/want

In principle, there are three types of thermostats to choose from. 

1. Mechanical or manual thermostats 

Mechanical thermostats are also known as “manual” or “non-programmable” thermostats. The main characteristic of a mechanical thermostat is that you have to manually adjust the temperature and turn your HVAC system on and off.

A digital manual thermostat offers arrow buttons to control the temperature, while an analog manual thermostat has a dial to change the temperature.

A problem with mechanical thermostats is that they might have up to a +/- 3-degree differential, while other types of thermostats only have a +/- 1-degree differential.

2. Programmable thermostats

The main characteristic of a programmable thermostat is that you can program it to keep your home at pre-selected temperatures during specific programmed times and days. This ensures a smaller utility bill every month. It is commonly believed that if you normally have a small to medium energy bill you can save up to $180 per year.

3. Smart thermostat

A smart thermostat is a “next level” programmable thermostat. The main characteristics of smart thermostats are that 

  • you can control it from your smartphone, tablet or computer, meaning that 

you can regulate your home’s temperature remotely,

  • they have touchscreen displays,
  • they can follow voice instructions,
  • they give you dirty air filter alerts, 
  • they can be programmed with schedules for various situations, and 
  • they have the ability to automatically regulate your schedules.

Step 2: Determine the compatibility with your HVAC system

The next step is to decide which brand and model you want to purchase.

To find the right model, check the compatibility.  Aspects you have to look at include the following:

  • Your HVAC’s voltage – determine whether it is a low voltage, millivolt or high voltage system.
  • The location on the wall – determine whether the new thermostat will fit in the same location as your current thermostat so that you can use the existing wiring. 
  • The number of heating/cooling stages your system has – meaning how many speeds your air conditioning and heating systems have.

Step 3: Contact an HVAC expert when in doubt

If you encounter problems with the steps the easiest way to get an answer to your questions is to contact your HVAC professional.

Do I need to shut off the power to replace the thermostat?

You must ensure that before you remove your thermostat from the baseplate no power is flowing to the thermostat or your HVAC system.  

What might happen if you replace your thermostat without turning off the power?

Your home uses 110 or 220 volts which poses safety risks. You can be seriously injured, and in extreme cases, even be killed if you work on electric wiring carrying 110 or 120 volts.   

Apart from the personal risks, you also put the thermostat and all the HVAC devices at risk if you don’t shut off the power before you start with the replacement procedure. The devices might be damaged, the wire could short out, or a fire could occur.

How do I shut the power off?

As the first step, you have to locate the switch controlling the flow of power to the heating and cooling devices in your home. 

Locate your HVAC system’s switch and turn it off

Some systems’ on/off switch is in the breaker or fuse box. Usually, this switch is labeled “HVAC” “Heating,” “Furnace,” or “Air Conditioning.” When you’ve found it, switch it to the “Off” position. Remember, if there are different switches for heating and cooling, put both switches off.

If the circuit breakers aren’t labeled, switch off the main breaker or remove the
main fuse. All power in your home will then be shut off. 

Test whether the power is off

It is always a good idea to check whether the power is really turned off before your start working on your thermostat.  The easiest way to test is to adjust the temperature on the thermostat by at least 5 degrees. In winter turn up the temperature and in summer turn it down. Wait at least 5 minutes and if the system doesn’t turn on, the power is definitely turned off. 

How to tell if my old thermostat is bad

Usually, thermostats need not a lot of maintenance, other than keeping them as clean and dust-free as possible. A thermostat can last for 10 to 12 years. Generally speaking, thermostats start to malfunction because their wiring has aged or dust has accumulated in them.

What are the signs that your thermostat is bad? I’ll discuss some of the most common indicators of a bad thermostat, but you’ll find more detail in “How To Tell If Your Home Thermostat Is Bad.” Common signs include the following:

  • Your heating system doesn’t switch off and is constantly running.
  • Your heating or air conditioning systems are not responding at all.
  • Your home’s temperature and the setting on your thermostat do not match.
  • The temperature in your home keeps fluctuating. 
  • You’ve recently experienced a huge increase in your energy bills.


Although it is possible to replace most thermostats by yourself, there are many reasons why it is perhaps not the best option in the long run. You might initially save on labor costs to do it yourself, but you make a calculated choice to do it. If something goes wrong during the replacement process or the thermostat encounters problems when the warranty is still valid, the manufacturer might not repair the thermostat or refund you.


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