What Gauge Wire for Thermostats? [Here Is the Answer]

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Choosing the right gauge wire for your thermostat is quite confusing, isn’t it? Also, there is a lot at stake because using the wrong gauge might lead to heat resistance, which might even escalate into a fire hazard.

So, what gauge wire for a thermostat will be perfect for your need?

Generally, 18/5 gauge wire is used for all kinds of thermostats. Because it is the safest option over 250 feet. If the wiring length is less than 250 feet, you can utilize 20 gauge wire. For the Nest thermostat, 22 gauge is recommended.

Still, a bit confused eh? I have explained all you need to know about choosing the right gauge wire for your thermostat here.

Now, let’s dig in and find out which one is exactly the right for your thermostat! 

Why Perfect Wire Gauge Is Important for Your Thermostat?

Depending on the installation, you’ll encounter two sorts of wiring. The two most common wire gauges will be 18 gauge and 20 gauge. 

The most straightforward technique is to select depending on length because anything up to 250 feet should be held by eighteen gauges. 

Though it is a widespread misconception, it is possible that the C-wire does not power the thermostat. But C wire is a must if you have a smart thermostat.

The power supply cables (sometimes called “hot” wires) are usually designated Rc (for cooling). And Rh (for heating). The control panel of the HVAC system provides a 24-volt power source.

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Source: Learn Metrics

Composition of the Thermostat Wire In HVAC applications, solid copper is ideal. Unless the wire is routed in a plenum, it doesn’t make a difference. Inside a plenum is an area where the air will be used to provide the structure’s air supply.

So the answer to your question about what gauge wire is a thermostat wire is not a single gauge. Rather sometimes, it depends on the length of the wire. By the way, while working with your home air you need to know the required size of the furnace blower motor.

What Is the Perfect Wire Gauge for Your Thermostat?

Thermostat wire comprises a bundle of 18 or 20-gauge copper conductors. Each conductor is coated with a protective, flexible coating of different thermostat wire colors

The wire gauge and the number of colored wires used vary. 18 gauge wires are somewhat thicker than 20 gauge wires.

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Source: Jackson Systems 

So, what is 18/5 wire?

The first number is the gauge of the wire which is 18. And the second is the number of individual copper conductors that are included inside the bundle. In this case, there will be 5 copper conductors.

At the thermostat, the thermostat wires emerge from the wall. And are stripped at the ends to reveal the copper within. Connections link the copper ends to the thermostat’s base. 

Let’s take a closer look at the wire gauge now so that you can choose it as per your needs.

18 Guage Wiring for Thermostat 

18 gauge wiring is the most common size since it frequently comes with five conductor wires. Low voltage stats and HVAC equipment have become the industry norm. For lengths up to 250 feet, 18 gauge thermostat wire is recommended.

I have compiled some of the best 18 gauge wires that I found people mentioning in the forum. You can use them as well in your thermostat.

WiresConductor wiresPrice
THE CIMPLE CO 18/8 Thermostat Wire8 wiresOrder Now!
Woods 18/5 Thermostat Wire5 wiresOrder Now!
Cableague Thermostat 18/5 Wire 5 wiresOrder Now!

In the United States, almost all HVAC systems are fueled by a 24V low voltage current. The only applications that do not use the 24-volt system are boilers and electric furnaces. Solid-fuel stoves and millivolt furnaces are also available. Everything else should run on 24 volts.

Other General Guage Wiring for Thermostat 

Other wire gauge sizes range from 16 to 20 gauge. 20 gauge wire is typically too thin to run large amounts of wire. However, it works well in smaller applications. When it comes to wire, remember that the thicker it is, the lower the electrical resistance. But you can use it for a lower distance range like less than 250 feet.

As a result, 16 gauge thermostat wire is a good choice. That is for stringing vast amounts of wire across a large structure or a residence. Because of its thickness, the only drawback with this size is fitting through socket plates.

Special Wiring for Nest Thermostat

The Nest thermostat requires wire gauges of 22 to 18 gauges. This is typical for home heating and cooling systems. Any wire thinner than 22 gauge may be detected and operated incorrectly by the Nest thermostat.

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Source: YouTube

The Google Nest Thermostat has made a revolutionary change in the thermostat industry. The user experience and savings on your bill have taken everyone by storm. You can try them as well. It’s really easy to control and more importantly saves almost 15-20% of your yearly bills. 

Also, you can go another step ahead and pick up a Google Nest Learning Thermostat. That Eco setting is the real difference-maker.

The highest amperage that a 22-gauge wire can transport is 0.92 amps. Handbook of Electronic Tables and Formulas for American Wire Gauge claimed this. You’ll need a wire with a smaller or larger gauge if the amperage is more than 0.92A.

So this is what the gauge wire for the nest thermostat should be. 

Which Gauge Should You Use?

We hope you’ve got a perfect idea about all types of wiring you can use in your thermostat. As different thermostats and different distances require different wiring so you need to choose wisely.

If you need wiring up to 250 feet, you should go for the 18 gauge wiring. Because 18 gauge wire is thicker it is commonly used. 

You can use 20 gauge thermostat wiring for a short range of less than 250 feet. As 20 gauge is thinner than other wires so it’s not safe for a longer range.

Then lastly, if you are planning to install a Nest thermostat 22 gauge will work fine. If you are suffering from choosing the perfect thermostat for you then let us help you. 

Ecobee3 Lite SmartThermostat, BlackCheck Deals on Amazon
Honeywell Home Home RTH6360D1002 ThermostatCheck Deals on Amazon
Google Nest Thermostat – Smart Thermostat Check Deals on Amazon

These are the most common and well-renowned thermostats in the market right now. You just must select according to your budget and preferences.

What happens if the thermostat is installed incorrectly?

It’s really important to install your thermostat perfectly otherwise, it can cause you an electric jolt. Additionally, the thermostat, electrical system, or even the AC/furnace unit itself might be destroyed.

Dual-fuel systems, a poorly situated thermostat, whole-house humidifiers, or faulty wiring are the basic faults. These can all make thermostat installation more time-consuming, annoying, and difficult.


Can I Use 24 Gauge Wire for a Thermostat?

No, you can not use a 24 gague wire for a thermostat. Because lighter wire produces too much voltage loss, the thermostat wire should be at least 18 AWG. A twisted pair cable is ideal for outdoor and remote sensors, but not for control loads. 

Can you use a bigger gauge wire than needed?

Yes, you can always use a larger gauge than what is required. However, make sure the wiring methods are proper.

Will CAT 5 Work for Thermostat Wire?

The thermostat wiring is Cat5. Many modern thermostats control humidifiers and other components if you’re running a longer connection than you need. Cat5 will very certainly work doubled up. So, it is safe to use cat5 as a thermostat wiring.


We hope you now have a clear understanding of what gauge wire for thermostat. Now I hope we have succeeded to let you know which wire you should use and why. Now you just need to choose as per your requirement. 

Please leave any additional questions concerning your thermostat in the comments area. In any scenario, we will do our best to assist you.

Till then stay safe while working with electric devices.


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