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    Why does a Smart Thermostat require a C-Wire?

    Old dial thermostat are very differently than modern smart thermostats. They did not need any power to work and therefore when replacing an old thermostat, you are very likely to find that it only required 2 wires.

    Today’s modern smart thermostats are more complex devices which are equipped with such things as:

    • Wifi and Bluetooth chips
    • Multiple Sensors temperature and humidity sensors
    • Color Displays

    What this means is that a smart thermostat needs a constant flow of electricity from the furnace to keep its circuits running. New technologies have led to amazing consumer products that have many more options then traditional products. Smart thermostats today are really quite smart! However, when it comes to installation the new requirements might cause problems for home owner.

    Why are Common Wires a Better Power Source

    Smart thermostats are like little computers. They can 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 smart thermostat improve your home’s energy efficiency. This little computer needs a source of power, which is why manufacturers began to implement the c-wire. The most common source of power today in smart home technology whether a smart switch, outlet or thermostat is the common wire, more commonly called the “C-Wire”

    It’s clear that this choice in the design of the new products was motivated by the additional stability of this solution. It is not as easy to smoothly run a smart thermostat without C-Wire. To keep the smart thermostats consistently up and running, even when one of the heating appliances in your circuit breaks down, you will need a thermostat that can use an alternative source of power. 

    One new method developed by some manufacturers allow modern thermostats to get their power from the two hot and cold wires that bring power to your heating appliances. This source of power is then used to charge batteries, which are then used to ensure the consistency of the system. 

    Quick Tip on battery-powered thermostats:

    Previously, there were many smart thermostat solutions that ran on batteries available on the market. Unfortunately as smart devices evolved, manufacturers moved away from batteries. As of today, battery-powered smart thermostats are very rare and those that exist have fewer features than those that work with a C-wire.

    Before jumping into the article, we recently publish a Honeywell wifi thermostat review. Please consider this budget-friendly thermostat when making your purchase decision.

    You might also like a fun blog posts on the Most Commonly Used Alexa Thermostat Commands!

    How to Check if Your Thermostat has a C Wire?

    To make a long story short, you can simply detach your old thermostat and verify whether a C wire was used in the previous thermostat. If no c-wire was used, then a c-wire was likely never ran to the thermostat electrical box. 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. 

    Finally check whether a c wire was passed to your furnace. It is possible that if your old thermostat did not need a a common wire, the wire was never pulled from the furnace to the thermostat. 

    Remember it’s very normal to not have a c-wire in older homes.  Before moving forward to listing the best no c wire thermostats we’ll look at what can be done to add a c-wire to your box and other options. This will require more work, but will allow you to purchase almost any smart thermostat on the market.

    Is it Possible to Add or Fix a C-wire?

    Yes, there exists a few solutions. They can provide a source of power if want to use a smart thermostat that does requires a C-wire in a house that doesn’t have the C-wire.

    The picture above is a Venstar add-a-wire. Is by far the easiest and best looking solution to retrofit your thermostat’s electrical box. his little device allows you to split the single power wire and add a common wire.

    We recommend you look into this solution first. 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 seems broken.

     More Solutions:

    1. Another solution is to run a wire from your furnace’s common wire to your thermostat. This is a  more complicated solution. I recommend hiring a professional electrician to perform this kind of work.
    2. Finally, the simplest solution is purchasing a power adapter for your thermostat. The power adapter simply plugs into a standard power outlet and can convert 110V/220V power to the low voltage equivalent of the C-Wire. Many manufacturers already include power kits in their standard package in case if your old system is not using c wire or not installed.

    In my opinion, this third solution is not ideal. Not only does it take up a power outlet in your home, but it also not great to have a long wire go down your wall. If you don’t have an outlet near your thermostat location this solution doesn’t work.

    3 Best Smart Thermostat No C Wire of 2021

    3. Lux Products GEO-WH Wi-Fi Thermostat

    Most User-Friendly

    With a minimal modern design, the Lux-GEO offers many great features a compact and easy-to-use product.

    0
    Smart Rating
    Price
    Low Cost
    Thermostat Features
    All basic features included
    Compatibilities
    Only with C-wire

    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.

    Amazon Rating
    3.3/5

    2. Ecobee SmartThermostat with Voice Control

    Best Mobile App

    From hardware to the mobile app. Ecobee offers the most high-end smart thermostat experience we've tested.

    0
    Smart Rating
    Price
    High
    Thermostat Features
    Large number of app features
    Compatibilities
    Highly Versatility

    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.

    Amazon Rating
    4.7/5

    1. Google Nest 3rd Gen Learning Thermostat

    smart thermostat no c wire

    Most Advanced Software

    Advanced mobile app with unique features. High cost with high value makes this our favorite thermostat.

    0
    Smart Rating
    Price
    High
    Thermostat Features
    Large Number of App & Thermostat Features
    Compatibilities
    Alexa Compatible

    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.

    Amazon Rating
    3.3/5

    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

    Final Thoughts

    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.

    Prices pulled from the Amazon Product Advertising API on:

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