Thermostat Wiring For Dummies

We put together a step by step guide on thermostat wiring. Learn how to do it yourself in the simplest way possible and in all safety.

Wiring a thermostat is a simple step by step process that anyone can do. Most of the process is about following safety procedures and avoiding common mistakes. Once you know what type of system you have, the hardest part is out of the way. For complex systems like heat pumps and multi-zones, a professional is recommended. These are in a completely different category altogether, so there is a lot of extra work that goes beyond the normal home repair. If you’ve never done wiring work before, this should still turn into a successful project. With a few tools and some time, you’ll have the thermostat wired in minutes.

Can This Method Be Used On Newer Wi-Fi Thermostats?

Yes! The only big difference you will see between the newer Wi-Fi models and older ones is an extra wire. The guide covers four and five wire designs, so the only thing holding you back is whether the original installation is compatible. Incompatible wiring (installing a new five wire thermostat to a four wire base) requires higher expertise, and in some cases professional help. You should never try to force one type of connection over another since it could damage the entire system.

Will Brands Have Different Wiring Instructions?

Very little will change with installation across any of the major or generic brands. Lux, Honeywell, Nest, White Rodgers and more use the same basic guidelines to hook up their four and five wire thermostats. It is still a good idea to skim through the directions and make sure nothing new pops up.

That missing bit of information could make the difference between a half functioning thermostat and a fully functioning one. But for the most part you won’t miss anything major when deciding between the different brands for thermostats. The only noticeable difference will be with quality and price.

Wiring A Thermostat For Dummies

An important thing to note is that the actual instructions for wiring thermostats is really a ‘cheat sheet’. Make it a point to print out the color guidelines and you will have everything you need to finish the wiring. Once you understand the wiring needs of the thermostat, it is a matter of putting A to B, and nothing too complicated. This guide works for replacements as well as upgrades, but only between the same wiring base. So four/four and five/five will be your workable limits when using these directions. All of the below information is assuming you are using new wires rather than reusing the ones already installed.

For Four Wires

The wires you’re going to need to know for this setup;

  • G – Fan (Green)
  • R – 24 VAC/Rc/R/Rh (Red)
  • Y – Compressor/Air Conditioner (Yellow)
  • W – Heat (White)

At this point you are going to play the match game. Start by looking at the letters and matching it with the labels. One end to the other, nothing fancy in-between. The colors are used to help further illustrate where each wire goes in case you get lost. So in short, the order or priority when installing is Letter>Color. Most setups will be just fine with letters, but if the print is a bit fuzzy, falling back to colors will help you to figure out where each wire goes.

For Five Wires
  • G – Fan (Green)
  • R – 24 VAC/R/Rc (Red)
  • C – 24 VAC Common (blue, brown, or purple are the most common)
  • Y – Compressor/air conditioner (Yellow)
  • W – Heat (White)

The main difference between the four and five is the common wire, which can only be found in the five setup. Colors vary by the brand, but brown, blue and purple are the most common. With the common wire, you get a piece that provides power from the transformer. So for obvious reasons, it is a wire that you don’t want to play around with or put in the wrong place. Take great care when attaching the common wire, double-checking every part of the interface that it is associated with. Once you get used to these configurations everything else will be second nature. Before starting any of this, turn off power at the breaker. This applies to both wire setups, so consider it mandatory even when you’re not handling the common wire. Wear protective gear just in case, although you can consider that part optional.

Using a magnifying glass is a good idea if the letters are too small for recognition. Common mistakes involve mixing up wires due to identical wiring or forgetting to turn off the breaker. Either one could damage your entire unit, costing you thousands of dollars in repairs. Don’t let a simple thermostat wiring dig into your budget when it can be completed in minutes. And if you’re ever confused about your specific thermostat, recheck the manual. That is the best way to check for anything you may have missed.

When The Product Won’t Turn On

The first thing you should do is check for any loose wires. If all the wires are in the correct place, the next step is to see if you mistakenly installed a four wire thermostat to a five wire base. When this is the case, you should immediately remove all wires since it can cause damage to the entire system. Leaving it in place will cost you extra money if something goes wrong, and lead to the hiring of a professional.

You should also check to see if there is a switch that needs to be on. For modern thermostats this may be the issue, which is common among the ‘smart’ options. At this point if it isn’t working, looking at the manual may lead you to the correct path. Thermostat manuals give all the necessary information in a ‘what if’ scenario when the product won’t turn on. And the good news is that it covers old and new installs, so there will always be something in there that you can use. When the manual fails to resolve the issue, then you need to consider looking at professional help to get the thermostat working.

Using The Old Wire

You can always use the old wire with a new thermostat. There are a lot of reasons to do this, and the directions follow the same previous guidelines. Since the older wires that are being reused may be a little worse for wear, wrap them with electrical tape. This will ensure that you don’t have any issues with the thermostat shorting out. If the wires short out it could ruin your brand new thermostat. Taking a few seconds to wrap old wires (or use new ones) is a small price to pay with your time.

Mistakes Made During Thermostat Wiring

Anyone can handle the wiring for a thermostat, but that doesn’t mean that carelessness won’t mess up the job. Even messing up the little things can have long-term effects that slowly degrade system performance. It’s important to approach this project like any other, regardless of the skill level required.

Not Turning Off The Fuse BoxSafety comes first, so forgetting the most basic safety measure will always bite you. It doesn’t matter what type of thermostat you’re installing, when dealing with wires there is always a chance of danger. With newer installation requiring even more than the five wire setup, safety should not be ignored.

Reusing Old Wire Without Checking ItThere is nothing wrong with reusing wire. Obviously you want to check for burn marks, liquid or any tears in the casing. All of this will let you know if there is a bigger problem with the system like a short. Wrapping old wire in electric tape protects you and the system from any type of past or future damage. It’s a cheap protective layer that is necessary for all installations.

Installing The Wrong Thermostat TypeAlways install a thermostat to its compatible base. So 4/4 and 5/5 when dealing with the wire setup. You can avoid a major headache later on that could damage your entire system. The major component to look out for if you don’t know the wiring system is the common wire, which is always absent from a four wire setup. The color will vary but the function will always be the same.

Cutting New WiresWhen purchasing wires separately from the thermostat, you have to cut/strip them so that they fit comfortably in the base. This isn’t a problem in itself, but becomes a problem when you strip the wires too short. It is better to have them longer than what is needed than too short to use. Long wires can be comfortably cut to a size that fits inside the thermostat. So when you have a choice, always take a long wire over a short one.

Ignoring The ManualIf there is a manual present, always check with it before starting an installation. There could be important information about turning on the unit for the first time. A lot of common questions are answered in the manual, and there is even telephone support available for new customers. This is likely something you won’t need, yet it’s something that is nice to have in a pinch.

Any of these things can lead to a bad installation, but they are all avoidable. Instead of memorizing the guide, print it out or have it with you during the install.

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How Long Does It Take To Install A Thermostat?

If you’re just doing the wiring and nothing else, then less than fifteen minutes. For a complete installation with base, you are looking at half an hour. So either way you are well under an hour for install, which isn’t half bad considering the complexities of the product. Getting a modern thermostat or smart thermostat won’t make installation go any faster. The benefits of those systems comes with integration into your wireless networks and home convenience equipment like an Echo. Even Google Home works well with the new age thermostats.

Can Anyone Install A Thermostat?

Yes, it really is as simple as stated. If you can follow directions, then you can handle thermostat wiring. It’s more about understanding where each wire goes rather than figuring out how everything works. No experience is necessary, you just need to be safe and read the guide. When things get too difficult, it has more to do with something going wrong with the system. Don’t go overboard with trying to figure it out, and instead look at getting professional help to complete the install.

Why Should Homes Have Upgraded Thermostats?

There are major benefits to having a modern thermostat in the home. The first benefit is always going to be controlling it with a digital interface, either manually or automatically. Cable and satellite providers now have home systems that target these new smart thermostats.

They work in conjunction with the rest of the devices on the Wi-Fi network and becomes a part of your entire system. A big selling point when cable/satellite companies push a connected home is how well they work with smart thermostats. When you get to smaller devices like Amazon’s Echo or Google Home, things get a little more interesting. Whichever connected home device you decide on, having a modern thermostat in the home will only enhance its usefulness.

Does Thermostat Wire Type Matter?

You’ll run into two types of wires depending on the install you plan on doing. Eighteen gauge wire or twenty gauge wire will be the two main choices. The easiest way to decide is based on length, as anything up to two-hundred and fifty feet should be handled by eighteen gauge. When you need a much shorter length, twenty gauge will do just fine. All of this is assuming a larger install of something like an HVAC thermostat, which is expected to have much more functions than a regular thermostat.

What Type Of Gloves Should Be Used?

Gloves are optional, but if you do want an extra layer of safety choose rubber. Any pair of cheap rubber gloves will do the trick. So in the unlikely chance something goes wrong, you’ll be protected from electricity thanks to the insulated rubber.

Let us know what you think of the information provided in this article.