Thermostat Detailed Replacement & Buying Guide

thermostat reviewSometimes, once you have something installed by a professional, you later learn how easy and cost-effective it would have been to do it yourself. While thermostat installation might look complicated at first glance, it’s actually among the simpler jobs a handy person might tackle. The task really amounts to selecting the proper unit, mounting the unit to the wall, and connecting the wires to the correct terminals. (Always shut off power to the HVAC system at the breaker box before doing electrical work.)

The instructions provided with a new thermostat will cover the actual installation, and manufacturers generally include a helpline phone number to use if you get stuck. Since installation is covered in those instructions (and plenty of YouTube videos), we’ll talk about mainly about how to find the right thermostat for your heating and cooling system.

Should I Replace My Old Thermostat?

This is an important question to ask because the thermostat currently in use might be good enough. There are two main reasons to replace a thermostat: either the old thermostat is broken, or the old thermostat can’t do the job the way you want it done.

Broken-related Replacement

If the old thermostat is broken, then the need to replace it is obvious. Sometimes, trying to determine whether the problem is with the thermostat or in the HVAC unit itself can be a challenge.  If the blower is not turning on, with a little effort you can bypass the thermostat and see if the unit turns on.

To do this, turn off the power to the HVAC at the breaker box. Thermostat covers are designed to be removed easily by hand. Remove the cover to expose the control wires. Sometimes there will be an additional cover that must be removed with a screwdriver to expose the control wires.

If any control wires are loose or disconnected, you may have already found the problem. Tighten everything down and turn on the power to see if the problem is gone. It isn’t necessary to replace the cover for this.If the problem hasn’t been corrected, shut off the power at the breaker box once more. Remove the appropriate wires from their terminals and twist them together.

Which wires are twisted together will depend on the problem is with a heater or an air conditioner. If your heater has the problem, the correct wires will be red and white. The wires will be red and green if the air conditioner has the problem. After twisting the wires together, turn the power back on at the breaker box. If the blower comes on, the thermostat is bad. If the blower does not turn on, the problem is somewhere else and it’s probably time to call a professional.

Performance-related replacement

Performance-related replacement can be a bit trickier. Higher-end thermostats can be programmed to manage the HVAC system under many different situations. Some of the newest thermostats, like Nest, will actually learn your tendencies and self-adapt.

Older thermostats using a dial or slider are imprecise and setting the thermostat is a completely manual process. There is no programming one of these units. Changing the settings to adapt to different conditions requires a person to be there at the recommended time. Changing the settings when nobody is home is obviously impossible.

No old manual thermostat will provide any information about your HVAC system. Newer thermostats can tell you when to change a filter and warn you if there is a problem. The self-adapting Nest has even more features to help save you money and minimize the time spent programming the thermostat.

Benefits of Upgrading

There are three main benefits you’ll see after upgrading to a modern thermostat: energy efficiency, comfort levels, and adaptability. We’ve touched on some of this already, but let’s look at each of these benefits in more detail.

  • Energy Efficiency – The energy efficiency of the HVAC system itself is largely set in stone based on the system you buy. The only control you have once your HVAC system is in place is the way you make use of the system. That’s where a modern thermostat can have a big impact, translating directly into savings on your energy bills.

Programmable thermostats allow your HVAC system to operate more efficiently by heating or cooling when people tend to be home, and reducing the output when people are away or asleep. Another newer type thermostat is called wifi thermosts which often come with the program function as well. For more information, you can read our related article: WiFi Thermostat Worth My Money?

  • Comfort Levels – With a programmable thermostat, not only can you use most of your heating and cooling energy when people are home to make use of it, these thermostats can be programmed to turn on at just the right time before people get home so the house is comfortable the moment you walk in the door.
  • Adaptability – You live a different life during weekends than during the week. On any given weekend, you might be home more than usual, or possibly away more than usual. Programmable thermostats allow for different operation during the weekend. If you invest in a Wi-Fi-enabled thermostat, you can even adjust the programming while you are away via a smartphone app.

What Type of Thermostat do I Need?

This is an important question to ask because different HVAC systems require different types of thermostats.

Thermostat Power Supply

This largely depends on the type of HVAC system you’ve got. The most common systems supply 24V, considered to be low voltage, and most thermostats will work for these.  Electric heating systems employ high voltages of 110V to 220V, and some older systems use a direct line wired into the home’s electrical grid. Finally, some gas and oil-fueled furnaces that don’t use any electricity depend on thermostats using 24 millivolt supply power. Clearly, it’s important to know what your system uses so you buy a compatible thermostat. Being wrong could damage the thermostat or the HVAC system.

HVAC System Fuel Source

Another piece of information you’ll need is how your heating system is powered. This is important because the wiring can be different for various types of systems. Some thermostats are only good for certain types. For example, a low-end thermostat may only be designed for a gas furnace and will not be able to control an electric furnace. Know what you need before going shopping.

If your home uses hot water for heat distribution, you’ll have a boiler most likely fueled by either natural gas or oil, but can sometimes be fueled by electricity or a heat pump.Furnaces can be fueled by natural gas or electricity. Electric heat plates and radiators are, as the name implies, powered by electricity.

Keep in mind also some older homes use direct heating, such as a wood-burning boiler, that were never intended to be used with a thermostat.

Most air conditioning units are powered by electricity, but very old systems might be powered by natural gas. There is an emerging trend returning to natural gas air conditioning, but newer systems are not very common at this time.

Labels attached to both the heating and cooling units should specify how they are powered, and you can always check the documents that came with the units.


A third important piece of information you need is how many stages your heating and cooling systems have. Some units are designed with multiple output stages so it can operate efficiently under various conditions.  Most systems have one or two stages, but some thermostats can control even more. Even if your heating unit has only a single stage, some thermostats will allow a secondary system to function as an additional stage.

If your system has only a single heating and a single cooling stage, anything from a very basic thermostat to a sophisticated self-adapting thermostat will get the job done. If you have multiple stages for either heating or cooling, then the thermostat you buy must be capable of controlling the number of stages your system uses.

Know your heating and cooling systems before you begin shopping for a new thermostat. Buying the proper equipment in the first place will help you avoid delay and sidestep significant problems.

How to Checking Heating and Cooling Stages
Different stages are basically different output levels. Some systems have only one stage—essentially just on and off. A two stage system will have a low and a high output stage, allowing the system to adapt to different conditions. A single stage unit might be supplemented by a different form of heating or cooling, such as baseboard electrical heating, that might kick in when the furnace alone can’t quite keep the house warm enough.
It’s simple enough to check how many stages your system has by looking at the wiring inside the thermostat. You can access these wires using the same process we described above in the section about determining whether your thermostat needs replacement.
On the heating side, look for white wires numbered w1 and w2, and in some instances possibly even w3.  A single stage heating system will not have more than one white wire connected to a w terminal.  On the cooling side, it’s the same story only the wires are yellow in color and lead to terminals marked y1 and y2.

Disposing of the Old Thermostat

One other detail that shouldn’t be overlooked is the disposal of your old thermostat. Older thermostats often made use of mercury switches to ensure clean electrical contact every time your HVAC system was turned on. Mercury is a metal that is liquid at room temperature, and it’s also quite toxic. Simply throwing the old thermostat into the trash is irresponsible.

A company called Thermostat Recycling Corporation has 3,400 collection sites across the contiguous 48 states. A collection site near you can be found by using their zip code search tool. Please be responsible and dispose of your old thermostat by properly recycling it.

Review for Top Programmable Thermostat Models to Consider

  • Emerson 1F80-0471 Programmable Thermostat – Easy to use and powered either by battery or wire, it retails for about $50. Programming is manual only, using 5 mechanical push buttons and a large display screen. It is compatible with most low-voltage systems.
  • Sensi Wi-Fi Programmable Thermostat, UP500W – This unit is programmed via Wi-Fi connection from computer or smartphone. It retails for about $110 and is powered by 2 AA batteries. It can handle 4 heating and 2 cooling stages and regulate room temperature within ±1˚ Fahrenheit.
  • Radio Thermostat Company of America CT50e Wi-Fi Thermostat – This Wi-Fi programmable thermostat allow up to 4 programmable periods per day, can handle 2 stages each of heating and cooling, and requires a C-wire to enable Wi-Fi.  The unit retails for about $105 and works with nearly every HVAC system. It comes with a USNAP module that, when inserted, displays Wi-Fi connection instructions right on the thermostat’s screen.

Review for Some Smart Thermostat Models to Consider

  • Honeywell Wi-Fi smart Thermostat – This unit can be programmed via Wi-Fi or using the touch screen. Powered via the c/g wire or using an external power supply, this thermostat can high-voltage heating and cooling systems, and heat pumps. It retails for about $170, is adaptable, and you can control the screen color to match your décor.
  • Nest Learning Thermostat, 3rd Generation – The Nest works with most 24-Volt HVAc systems and can handle 3 heating and 2 cooling stages. The smart features detect when a person is in a room and can turn of and off features based on that information. Retailing for about $250, it requires a separate 110V power supply. It is controlled only via Wi-Fi connection from smartphone or interface on the nest website.

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