A thermostat is usually one of the first intelligent devices that people add to their home. The main reason for this is the convenience and comfort of arriving home to a house set at the perfect temperature. Even better, you save money on utilities since the thermostat automatically adjusts the temperature when you are away. Some units even monitor your adjustments and automatically adjust the schedule to match your preferences.
Before you click the buy button, there are a number of things you need to pay attention to when choosing a thermostat.
Line Voltage vs. Low Voltage
Most heating and cooling systems use low voltage thermostats, which draw 24-volts of electricity. These thermostats run most modern systems like furnaces, heat pumps, and many boilers. The wires are usually 18-gauge and have 2, 4, 5, or 8 conductors (each of which has a different color jacket). 18-gauge wire is fairly thin with a diameter of only 0.04″. If your thermostat has thin wires that connect to a terminal block with coded terminals then you have a low voltage thermostat. In this case, you have a few great options for your smart thermostat. The next step is to make sure you have a common wire.
However, electric baseboard heaters and convectors require a line voltage thermostat that can handle 120-volts of electricity. Some radiant floor systems also use line voltage controls. You can recognize line voltage thermostats because the wires are much thicker at either 14-guage (0.06″ diameter) or 12-gauge (0.08″ diameter). These wires are not connected to a terminal. Instead, they are tied directly to the line voltage wires serving the electric heater. If you open your thermostat and see wires connected with wire nuts then you have a line voltage thermostat. You can also look for the voltage label on your old thermostat. If you see 110V or 120V then you have a line voltage system.
Make Sure You Have a Common Wire
WiFi thermostats require a constant flow of power to keep the WiFi connected and the colorful display operating. The common wire gives the thermostat a continuous supply of 24-volts of power. Some simple or older systems may not have a common wire. We have a very detailed article about thermostat common wires, which helps you determine if you have a common wire and what to do if you determine that you don’t have one.
If your current thermostat has a wire connected to the C terminal (it is usually black or blue) then you have a common wire and can use any low voltage WiFi thermostat. If you don’t see a wire connected to the C terminal then be sure to check in the wall to make sure the wire isn’t simply disconnected. You can also check the circuit board at your HVAC unit to see if there is a wire connected to the C terminal.
HVAC System Compatibility Check
We just talked about checking your wiring, but before you make a selection you should do a final check to make sure your HVAC system can work with your selected thermostat. Check out the manufacturer’s website and use their compatibility tool. All of the big manufacturers have them. This is especially important if you have an HVAC system other than a furnace, boiler, or heat pump. However, we recommend that you check no matter what type of system you have. Each of our reviews have a link to the manufacturer’s compatibility checker.
Once you have confirmed your wiring situation, it is time to think about the features you want.
Important Features in a Smart Thermostat
Low voltage smart thermostats usually have very similar features so you should be good with any choice. Line voltage thermostats have fewer features, but they are catching up quickly. Let’s review some of the key features that you will see.
Small apartments can function with a single thermostat. However, multi-story or very large homes tend to have multiple heating and cooling zones that operate independently. That way, you can have the heat set to one temperature upstairs and a different temperature downstairs. If you have multiple zones then you will have to purchase a smart T-stat for each zone.
The way multiple zones work is that the thermostat wires all go back to a central zone management system. That controller reads each thermostat signal and then tells the HVAC equipment what zones need to be activated so that dampers or valves can be adjusted. There are occasional compatibility issues with older zone controllers. We recommend doing a quick internet search for the model number of your controller and the thermostat you are considering. You will probably be OK, but there is a chance that you may have to purchase a new zone controller for a couple hundred dollars.
Some manufacturers are working on true multi-zone system that includes a central control panel plus a series of zone sensors. However these aren’t widely available in North America at this time.
Extra Temperature Sensors
You may find that you have hot or cold spots in your home. This can happen when the thermostat is located in a central hallway, but an occupied room gets more/less sun or has poor insulation. The thermostat senses that the temperature is fine, but you are uncomfortable.
The solution is to install remote sensors, which send temperature information back to the thermostat. You can then program the system with priority information for different times of day. For instance, you might tell the thermostat that its internal thermometer should control the system during the day. However, at night you can tell the system to pay attention to the remote sensor in your bedroom.
Some remote temperature sensors, Ecobee for instance, also have a built in motion sensor that will prevent the system from going into Auto Away mode. If your thermostat is in an area of your house that people don’t walk past then it might think you are away and adjust the temperature accordingly. All of the sudden you feel uncomfortable, realize the system thought you left the house, and now you have to wait for the temperature to return back to the right setting. Remote motion sensors can help resolve this.
Remote sensors have a low-power radio that talks to the thermostat and they have a replaceable battery that lasts for a year or more.
Nest has an interesting feature that allows you to skip manual programming. All you do is turn the temperature up and down for about a week and the Nest programs itself based on your preferences. It isn’t a perfect feature so most people go back and make adjustments to the settings. However, this can save you a bit of time and frustration when first starting out.
We don’t think this is a critical feature to have since most people already know what temperatures they prefer at different times of day. In addition, the apps provided for the thermostats make it very easy to adjust the programming. However, if you just want the thing to program itself then be sure to go with a learning thermostat.
Energy Saving Suggestions
Many people like to receive regular reports that help them understand how much money they are saving. These reports also help people strive to save more money on their utility bills — it is like turning your thermal comfort into a game. All of the thermostats that we recommend track your energy usage and provide a report that helps you achieve more savings.
As software improves, we expect more features that help people save energy, which obviously saves you money.
Automatic Home/Away Adjustments
Most of the smart thermostats on the market have motion detectors in them so they can determine that you aren’t home and automatically adjust the temperature. This is great for when you forget to adjust the temperature before going on vacation or when you are home in the middle of the work day. It can also be a bit annoying if the thermostat thinks you are home or away when you aren’t. However, a few dollars of energy savings might be worth having this feature.
If your T-stat is located in an area of your home that doesn’t see a lot of foot traffic then you may want to turn this feature off. The other option is to select a manufacturer that sells remote sensors that can also detect motion, like Ecobee.
You can set your smart home apps to monitor your location (via your cell phone) and perform certain actions when you in specific places. For instance, you can program your thermostat to adjust the temperature when you leave work after 4PM. That way, the temperature starts to adjust before you arrive home. Geo-fencing is the name of the feature that runs a program when you physically enter or leave a digitally “fenced area.”
We think geo-fencing is important for some smart home devices like lighting, where you want to turn the lights on when you pull in the driveway. However, we don’t think it is a critical feature for thermostats. In fact, it can be quite confusing and can lead to more energy use. Based on our previous example, let’s say you program your thermostat to adjust the temperature when you leave work after 4PM. However, tonight you are meeting some friends for dinner from 5PM to 8PM. Now, your HVAC system will be running unnecessarily for 3 hours.
Now that you’ve identified the features you want in a smart thermostat, it is time to consider your smart hub. You can use a thermostat app so you don’t necessarily need a hub. However, if you want to control all of your different smart home components from a single app then you want to make sure your thermostat works with your chosen hub. Our thermostat review pages give you info on what hubs and systems each T-stat works with.
ENERGY STAR Rating
ENERGY STAR is a US EPA program that helps people save energy by developing criteria and certifying products. All smart thermostats will help you save energy so this isn’t a major criteria. However, the ENERGY STAR rating means that the thermostat meets strict energy saving guidelines. You can read more about the thermostat guidelines at the Energy Star website. Here are the requirements that manufacturers need to meet in order to be certified:
- Work as a basic thermostat in absence of connectivity to the service provider.
- Give residents some form of feedback about the energy consequences of their settings.
- Provide information about HVAC energy use, such as monthly run time.
- Provide the ability to set a schedule.
- Provide the ability to work with utility programs to prevent brownouts and blackouts, while preserving consumers’ ability to override those grid requests.
There are a lot of state programs that offer a rebate for purchasing a programmable thermostat. Be sure to check your electric or gas utility’s website for rebate information. In addition, each thermostat manufacturer has a page on their website dedicated to rebates. Make sure you take advantage of these programs when you make a purchase because you can save around $100 (or more) for a programmable WiFi thermostat.