How to Install a Thermostat: Step-by-Step Guide
Replacing a thermostat is one of the most common home electrical upgrades among homeowners and do-it-yourself (DIY) enthusiasts. This is partly because the installation is usually pretty straightforward. However, given the stakes, it’s crucial to approach it carefully.
Modern thermostats improve comfort, efficiency and energy savings. They play a pivotal role in heating, ventilation and air conditioning (HVAC) systems by measuring and maintaining set temperatures. Mistakes in wiring or other components of installation can cause damage throughout HVAC systems, leading to discomfort and potentially hazardous environments.
Below, we’ll explain how to install a thermostat safely so that you can proceed with confidence.
Before You Begin: What to Know About Thermostat Installation
Unlike some other repairs and maintenance work, thermostat installation is something that many homeowners can do on their own fairly comfortably.
Before even attempting to install a new thermostat, however, it’s important to understand the fundamentals: the kinds of thermostats there are and which you need. It’s also important to appreciate compatibility requirements that could come into play mid-install.
Last but not least, you should secure all the tools and materials you need prior to starting.
Types of Thermostats
Many years ago, there was little variety in the kinds of thermostats that people had in their homes. All thermostats were simple, manual devices that homeowners needed to adjust by hand. Nowadays, there are other options available that can help you save energy and cut costs.
The three best kinds of thermostats to look out for, per Consumer Reports, are:
- Programmable thermostats – Programmable thermostats allow you to set specific temperatures for certain times or according to intervals. They generally don’t connect to the internet and are simpler than smart options, but offer less convenience.
- Smart thermostats – Smart thermostats offer much greater control over your home’s temperature with the ability to make adjustments remotely. Some options also allow for more intricate functions, like data tracking to further optimize temperatures and schedules.
- Mini-split thermostat hybrids – These devices offer additional coverage for homes that use wall-mounted heating pumps or “mini-split” options. They communicate with ACs and other devices via infrared signals, provided there’s a line of sight.
Of these, a programmable thermostat is the most straightforward. In fact, the Department of Energy (DOE) recommends programmable thermostats and provides guidance on installing and operating them. Smart thermostats offer the same functionality with added control, but they can be more complicated to set up. However, they may be easier to operate long-term.
In our steps below, we assume you’re using one of these modern options rather than manual.
Compatibility Considerations
As noted above, there are some complications to consider when installing a thermostat. Most of these involve compatibility issues and potential safety or efficiency concerns stemming from the HVAC infrastructure and electrical environment in your home. Programmable thermostats are recommended in most cases and are a big part of the DOE’s overall energy efficiency guidance, but there are some situations in which they (or their smart counterparts) may not be ideal.
For example, per the DOE’s guidance, programmable thermostats are not recommended for homes that have heat pumps due to potential inefficiencies. There are also considerations for electrical resistance systems (e.g., baseboard heating) that require special configurations like line-voltage thermostats, which, to date, can be somewhat hard to find and/or expensive.
Thermostats that have smart functions typically require a common wire (“c-wire”) to operate, and not all homes will have one in place already. This could mean that a smart option is not on the table, or it may be a reason you need to bring in a professional.
Being aware of these and other potential compatibility issues is just as important as knowing what the installation process requires and having the tools you need for it ready to go.
Tools and Materials You’ll Need
Here are the most important tools you’ll likely need as you install a new thermostat:
- The new thermostat and mounting hardware
- A screwdriver (ideally with multiple heads)
- A drill (if mounting a new base plate)
- A voltage tester for safety assurance
- A wire stripper, pliers and wire labels
- A smartphone (for smart thermostat setup)
It can also be helpful to have other DIY basics like a hammer, putty knife, electrical tape and marking tools (e.g., a pencil). Areas around the thermostat may need minor touch-ups after installation, so access to paint and painting tools like a brush, tray and dropcloth can also help.
With all of these things in place, you’re likely ready to put in a new thermostat on your own.
Step-by-Step: How to Install a Thermostat
As noted above, the installation process for a new thermostat is fairly straightforward. In the absence of compatibility issues or other complications, many homeowners can do it themselves.
Here’s a quick overview of how to install a thermostat, at-a-glance:
- Turn off the power
- Remove the old thermostat
- Disconnect and prepare wires
- Install the new mounting plate
- Connect the wires
- Attach the thermostat and restore power
Below, we’ll explain each step in greater detail.
Step 1: Turn Off Power
Before even thinking about taking your old thermostat out or putting the new one in, you need to shut off the power to the thermostat (and/or the entire HVAC system) and make sure it’s off.
Your electrical service panel should have clearly marked breakers for various areas of your home, and the HVAC/thermostat should be one of these. If it’s not clearly marked, consider testing breakers to see which is which or calling an electrician to determine and label breakers.
As you confirm that the power is off, you can also confirm that the voltage your new thermostat needs is being supplied by the existing breaker and won’t exceed the total specified voltage.
Step 2: Remove the Old Thermostat
Once the power’s off, you’re clear to start working on sensitive components. However, you should still use a voltage tester at this stage to ensure there are no unexpected live wires.
Most thermostats have a cover plate that needs to be removed, along with screws that fasten it to the wall. Take a picture before removing any components (even screws) to make sure you remember how everything fits. Frame your picture so that the wiring configuration is clear and easy to analyze visually, and label wires prior to removing them.
With these prep steps done, you can remove the thermostat base completely. But you should keep it nearby in case you need to temporarily reinstall it or if any other complications arise.
Step 3: Disconnect and Prepare Wires
After clearly documenting and labeling wires, you can start removing them carefully. This involves moving wires that will still be used into secure locations where they won’t get in your way or fall back into the wall. Consider using tape to secure your labeled wires against the wall so they’re easy to locate and reconnect later.
Step 4: Install the New Mounting Plate
With the old thermostat base out, you can get the new one in position to be connected. Make sure the base is level first, then mark and drill anchor holes (if needed). As you position the base, snake all the wires through so that they can be connected.
After the base is in place and the wires are through, inspect them to ensure all sheathings are fully intact. If your thermostat uses batteries, make sure there’s clearance to get them in easily.
Step 5: Connect the Wires
This is a simple step, but it’s one of the most sensitive and important ones. Using the markings from earlier, match the labeled wires to their corresponding connections in the new terminal and secure them properly. Consult any documentation provided by the manufacturer to ensure that wires are where they need to be, and visually confirm that there’s no exposed copper.
If you have any uncertainty about this process or are uncomfortable handling wires and connections, consider calling an electrician or other professional to handle this for you.
Step 6: Attach Thermostat and Restore Power
Finally, it’s time to put the finishing touches on your new unit. Simply attach the remaining thermostat base and/or cover to the mounting plate by snapping it on or using whatever other fastening mechanism the manufacturer provided—but consider taking a photo beforehand.
When the unit’s closed up, you are free to turn the power back on and see if it works. There may be some configuration to do, either on the device itself or via a companion app if it’s a smart thermostat. Once that’s sorted, you can start setting and testing HVAC functions.
Installing a Smart Thermostat: Additional Considerations
If the thermostat you’re installing is a smart option with internet connectivity, there are some additional resources and steps you may need to account for. For instance, you’ll likely need a c-wire. You also need a Wi-Fi setup with connectivity throughout the home, especially wherever your new thermostat is located. With a smartphone or other device, you can download and use a companion app both during setup and throughout the lifespan of the thermostat.
Smart thermostats may require firmware and other updates, both out of the box and at later dates, so some technical literacy may be required of anyone who interfaces with the device.
Issues with these necessities are signs you might need an electrician.
Common Thermostat Installation Mistakes
Even a relatively straightforward installation process has possible points of failure and issues that can arise. It’s important to stay ahead of these and use a level, careful pace.
Some of the issues homeowners and DIYers commonly fall into are:
- Forgetting to turn off the power prior to disconnection
- Mislabeling or completely forgetting to label the wires
- Configuring heat pumps and HVAC components incorrectly
- Failing to secure wire connections properly (i.e., too loose or too tight)
- Skipping system compatibility checks prior to purchase or installation
Being aware of these pitfalls upfront is half the battle, and practicing caution and attention to detail mid-install is absolutely critical.
When to Call a Licensed Electrician
Independent of mistakes and pitfalls, there are also some clear-cut situations where contacting a professional is either required or highly recommended. The most common of these is when you need a c-wire for your new thermostat, but there isn’t one present from the prior install.
Another common reason to call in a residential services expert is when you need to replace a line-voltage thermostat, or when you can’t be certain about voltage requirements due to unclear or non-existent documentation. Relatedly, older homes with complex wiring can make all kinds of electrical upgrades harder for DIYers, even relatively simple ones like thermostats.
If your HVAC system isn’t responding after installation, or if changing an electrical panel is part of the process, there’s no shame in calling in an expert to ensure ease, safety and efficiency.
Thermostat Installation in St. Louis Homes
Installing a new thermostat is a fairly straightforward process that many homeowners and DIY enthusiasts can tackle. However, issues with compatibility or older wiring can create challenges. Not to mention, there are other benefits to hiring a pro, like easily bundling other electrical upgrades or HVAC work along with a thermostat replacement.
If you’re going to bring in outside help, be sure to find a trusted partner who’s well-versed in code compliance and safety precautions. Brda Electric has handled residential electrical services for over 35 years. We’ll ensure safety and efficiency to keep your home and loved ones secure.
Contact Brda Electric for a safe, professional thermostat installation.