TL;DR: There are 2 easy solutions to installing a smart thermostat, without passing a new common wire (c-wire) through your wall. Either use an c-wire adapter in your electrical box (read below) or use a smart thermostat that doesn’t require a common wire (see top 3 at bottom of page)
Why does a Smart Thermostat require a C-Wire?
Old dial thermostat are very different than modern smart thermostats. They did not need consistent power to work. When replacing an old thermostat, you likely will find only 2 thermostat wires, which is a problem if you’re installing a new smart thermostat.
Today’s modern smart thermostats are complex devices equipped with:
- Wifi and Bluetooth chips
- Multiple Sensors temperature and humidity sensors
- Color Displays
- Google Assistant integrated
Smart thermostat needs a constant power. A flow of electricity usually pulled from an outlet to keep its circuits running. When I installed my first smart thermostat I thought it would be as easy as plugging-in my new device. Unfortunately, some additional wiring is required.
But don’t worry it really isn’t that difficult!
Why are Common Wires a Better Power Source
Before getting into the DIY installation instructions your new device I’m sure you’re a little curious about this new wire. Here’s the low down.
Smart thermostats are like little computers. They can do cool things like retrieve local weather data from the internet to ensure rooms inside are always well heated or cooled. They can even track when you’re in or out of your home to only turn on use energy when you’re on your way home. With such amazing features, it’ll come as no surprise that new sensors on programmable thermostats improve your home’s energy efficiency.
This little computer needs a source of power, which is why we need the common wire, more commonly called the “C-Wire”. Some thermostats run on internal batteries, but do you actually want another devices running out of batteries in your homes? I know I don’t!
Step 1: to Check if Your Thermostat has a C Wire
The first step of our installation guide is to make sure you actually don’t have a C Wire. Simply detach your old thermostat and verify whether a C wire was used in the previous thermostat. Here are some tips to help you understand what you’re looking at:
- Thermostats with C-wires will have a terminal with the name “C” next to it.
- If you have c-wire there will be 4 wires in your box: Black and red hot and cold power wires, a green ground wire and a c-wire.
- If you see 2 wires (red and black) or 3 wires (third wire is usually green or copper), none of these are your C wire.
Remember it’s very normal to not have a c-wire in older homes.
Easily Power Your Thermostat With a C-wire Adaptor
C wire adaptions, also called a power extension kit bring the extra power required by your new thermostat. The picture above is a Venstar add-a-wire. It is by far the easiest and best looking solution to retrofit your thermostat’s electrical box. This little device allows you to split the single power wire and add a common wire. The installation of such a c wire adaptor is also quick and easy. They can easily be purchased on amazon at the same time as your thermostat.
We recommend you look into this solution before going through the hassle of passing more wires. As this can be a tight fit in an electrical it might require that you purchase a larger box. The add-a-wire is also a great solution if the c-wire is broken.
If you opt to go with the simpler option of buying a smart thermostat that doesn’t require a continuous power source, we’ve compiled a list of our favourite devices in 2022.
Step 2: Pick a Thermostat that Works Without C Wire
3. Lux Products GEO-WH Wi-Fi Thermostat
The Lux GEO-WH Wi-Fi Thermostat is one of those great simple products. It offers all the minimum features we expect with modern smart thermostats. At its lower price point (99$ as of writing this article) it is among one of the best cheap smart thermostats that doesn’t require a c wire requirement.
As is the case with many large smart thermostat manufacturers, Lux Products has its own Android and Apple app to control temperature settings and is compatible with Amazon Alexa. One disadvantage is that the Amazon Alexa feature only functions when the thermostat is connected by C wire. The reason for this is most likely that functions that use wireless connection require a lot of power. Hence, the high power requirements aren’t feasible when the thermostat runs on batteries.
Overall, the minimalist design lower price point make this smart thermostat a very interesting option for systems that don’t have a c wire.
2. Ecobee SmartThermostat with Voice Control
The Ecobee Smart Thermostat with Voice Control is another amazing product that works without a C-wire. It can use as a power source both lithium batteries and an electrical outlet using a power adapter included in the box. Given the available power source options on this device, it is one of the most versatile smart thermostats, which should work in any new or old home.
It has other notable features, such as its ability to function with up to 32 room temperature sensors and built-in compatibility with Amazon Alexa. This opens the door to using some if this thermostat’s unique voice command features.
In addition, using the Ecobee app, allows you to gain access to many features. These include:
- Remote access to all thermostat settings
- Implement energy-saving temperature schedules
- Connect to additional Ecobee devices, such as lights, cameras, alarm systems
According to the manufacturer, the smart features of this device can save you up to 23% on heating and cooling bills in a year. Don’t forget that these elegant little devices will also add a level of style to your home.
1. Google Nest 3rd Gen Learning Thermostat
Google Nest 3rd Gen Learning Thermostat is among the most feature-packed smart thermostats available on the market. It appeared a few years ago and has since seen many upgrades so that Google is now building the product’s third-generation. It’s equipped with powerful features, a gorgeous multi-colour display and in our opinion a fun futuristic look. This is the only thermostat in the market that works without C-Wire and is compatible with most new heating and cooling system.
This thermostat usually gets its power through the hot and cold wires. Given that we couldn’t find an exact compatibility list, if a power cycling issue arises, it will always be possible to setup this thermostat with a power adapter.
One key differentiator of this product is its AI-based learning. According to Google, this feature allows the thermostat to improve its efficiency overtime. The Google Nest 3rd Gen thermostat takes outdoor and indoor temperature readings and finds the most comfortable and cost efficient way to reach your desired temperature settings.
Some additional smart features includes custom temperature settings for each person in the home, as well as multiple room sensors that can all centralize their temperature readings to a single thermostat.
Step 3: Install Your New Thermostat
How Long Does an Installation Process Take?
The installation of a wifi thermostat with no c-wire is a surprisingly easy process. The process can be separated in 2 parts: Wiring & hardware installation and app & software installation.
The removal of the old thermostat and wiring of the new thermostat itself can take as little as 15 minutes if you have previous experience with similar electrical tasks. The process can be a little longer if this is your first time working with wires. As long as you have the right tools, anyone can install their smart thermostat.
Before starting this work, make sure you know how to shut off a breaker and check for current. The most basic tools needed will be a Phillips head screwdriver and pointy pliers to manipulate wires. Longer handles are better than shorter ones to get to the hard to reach places.
Are Certain Kinds of Thermostats Harder to Install?
Yes there are some thermostats that are more difficult to install than others. If you plan to control multiple appliances with your thermostat, this will require more time. Not all thermostat can control multiple zones. However, if you are using a thermostat designed to control one heating appliance, such as a board heater, this thermostat will be very straight-forward to install.
In addition, a hybrid system that has heating and cooling appliances connected to it will require a more complicated installation. Not only is the wiring more complicated. but the software used to program them can also be more confusing for first time users.
Here is a link to our full guide on installing a smart thermostat.
I recommend you choose the option that fits your most important criteria. Are you looking for the best looking smart thermostat, the cheapest smart thermostat or the one with the most features? Once you’ve decided what’s important for you and properly established that you need don’t have a C-wire review the above products and make your pick.