A smart thermostat is a Wi-Fi thermostat that follows a schedule or learns one, lets you change the temperature from your phone, and can ease off heating and cooling when nobody is home. Whether it is worth buying comes down to three checks: it works with your heating and cooling equipment, you will actually use the scheduling and away features, and your current habits waste energy (a thermostat held at one temperature around the clock, for example). The price tag is the smaller part of the decision. [1]
Heating and cooling are where the money is. ENERGY STAR says almost half of the annual energy bill goes to heating and cooling, which it puts at more than $900 a year. [2] A thermostat decides when that equipment runs, so it is one of the few small purchases that touches the biggest part of your bill. The catch is that published savings figures vary widely, and the biggest numbers come from the companies selling the devices. This guide sorts the claims from the evidence and gives you a short checklist for buying one.
- The 8% heating and 10% cooling runtime reduction is the ENERGY STAR minimum for certification, not a promise about your bill. [3]
- The largest savings numbers (Nest and ecobee) are manufacturer claims, and ecobee’s footnote says its figure lacks independent verification. [4]
- Check voltage, the common wire, and heat pump support before you buy, and turn the power off before swapping.
- A setback schedule is where savings come from: DOE cites as much as 10% a year for 7 to 10 degrees over 8 hours a day. [5]
What a smart thermostat actually does
A basic thermostat holds the temperature you set. A programmable one repeats a weekly schedule you enter. A smart thermostat adds a connection to your phone and a layer of automation on top. DOE describes the practical difference plainly: smart thermostats are generally easier to use and have more reporting and interactive features than programmable thermostats, while programmable models cost less. [5]
The features that can change how much energy you use are few. You can set the system to ease off while you are away, change it remotely when plans change, and in many models the thermostat works out for itself when the home is empty. [1] Everything else, from weather screens to voice assistants, is convenience.
- Scheduling: temperatures that change by time of day and day of week, set once and forgotten.
- Away detection: the thermostat notices an empty house through its sensors or your phone’s location and eases off.
- Remote control: you can fix a forgotten setback from a parking lot instead of heating an empty house for a week.
- Reports: runtime history that shows how long the system ran, which is useful for spotting a system that never shuts off.
What the savings evidence says
There is no single trustworthy number for smart thermostat savings, and any article that gives you one is hiding the spread. The sources fall into three groups: certification thresholds, simulations, and manufacturer claims.
Certification. To earn the ENERGY STAR label, a smart thermostat has to show that the lower 95% confidence limit of the weighted national average runtime reduction is at least 8% for heating and at least 10% for cooling. [3] That is a minimum bar for the label, measured on runtime of the equipment, not a promise of 8% or 10% off your bill.
Simulation. A Lawrence Berkeley National Laboratory simulation of an idealized thermostat algorithm found that on average 5-10% energy savings are possible, with some homes able to exceed 20% but probably with some discomfort to the occupants. [6] The same result points to something useful: the largest savings in that simulation came with more discomfort, which suggests the setpoints matter more than the gadget.
Manufacturer claims. Google says that on average Nest customers save 10-12% on heating and 15% on cooling, which it translates to $131-145 a year, based on bill data from customers in 41 states. [7] ecobee advertises savings of up to 26% from an in-house review, and its own footnote says that method has not yet undergone independent third-party verification. [4] Treat both as marketing figures, useful for scale and not for payback math.
Check compatibility before you buy
Most returns happen because the thermostat does not match the equipment, not because it is a bad device. Spend ten minutes on this before ordering. Start by taking a photo of the wires on your current thermostat and of its model label, because both will matter.
Turn the power off first
Switch off the heating and cooling system at the breaker or the equipment’s service switch before you remove the old thermostat. If you see unfamiliar wiring, bare or brittle conductors, or high-voltage connections, stop and call a licensed electrician or HVAC contractor.
- Voltage. Standard furnace, air conditioner and heat pump systems use low-voltage control wires. Electric baseboard heaters and some wall heaters run on line voltage and need a thermostat built for it. A low-voltage smart model on a line-voltage circuit is a safety problem, not just a failed install.
- Power wire. Many smart thermostats want a common wire (often labelled C) for constant power. If your wall has no spare wire, the manufacturer may offer an adapter, and a heating and cooling contractor can run one.
- Heat pumps. A heat pump needs a thermostat that knows how to handle it, including the reversing valve and backup heat stages. DOE warns that if you have a heat pump you should not use deep setbacks without a smart or programmable thermostat designed for heat pumps, and that you should avoid any setback that triggers backup electric-resistance heating. [5]
- Multi-stage and zoned systems. Two-stage equipment, humidifiers, and zone panels each need specific terminals. Check the maker’s compatibility checker against your wire labels.
- Wi-Fi. The thermostat needs a stable signal where it hangs. A weak signal means missed schedules and a phone app that says offline.
Features that earn their keep, and ones that do not
Because the savings come from running the equipment less when comfort allows, judge each feature by whether it reduces runtime or makes it easier for you to keep a good schedule.
- Worth paying for: a clear schedule editor, reliable away mode, heat pump support if you have one, remote access, and ENERGY STAR certification, a common benchmark for smart thermostats (the current specification took effect January 1, 2017). [2]
- Nice to have: remote room sensors, which help if the hallway thermostat reads colder or warmer than the rooms you actually use.
- Mostly convenience: voice control, weather displays, and integration with other smart home gear.
Set it up so it actually saves energy
A smart thermostat saves nothing if it holds the same temperature all day. DOE’s long-standing rule of thumb is that you can save as much as 10% a year on heating and cooling by turning the thermostat back 7 to 10 degrees Fahrenheit for 8 hours a day. [5] That is a ceiling, not a guarantee, and it applies to the fall and winter setback for most systems.
Use that as your starting schedule: a lower setting while everyone is asleep or out, and a return to your comfort temperature shortly before you wake or arrive. Give the schedule two weeks before judging it. If rooms feel cold on return, move the recovery time earlier instead of raising the setpoint all day. In summer, a ceiling fan lets you raise the thermostat about 4 degrees Fahrenheit with no loss in comfort, according to DOE. [5]
Turn on any learning or auto-away feature, but check the first week of behavior. If the thermostat keeps deciding the house is empty while you are home, loosen the sensitivity or switch to a manual schedule.
When a smart thermostat is not worth it
If you already use a programmable thermostat with a schedule that matches your life, upgrading may add convenience and little else. Programmable models cost less, and DOE says smart models are generally easier to use and add reporting and interactive features. [5] The same goes for a home that is nearly always occupied, or a household that will not touch the schedule once it is set.
A smart thermostat also cannot fix a leaky, under-insulated house or an oversized system. If the real problem is drafts or a furnace that cycles constantly, fix the cheaper building problems first and add the thermostat afterward.
FAQ
Do smart thermostats really save money?
They can, mostly by running heating and cooling less when you are away or asleep. ENERGY STAR certification requires at least an 8% heating and 10% cooling runtime reduction at the lower confidence limit, but that is a certification threshold. [3] Savings depend on your climate, equipment, and how wasteful your old settings were.
Is a smart thermostat better than a programmable one?
Not necessarily. DOE says smart models are generally easier to use and offer more reporting and interactive features, while programmable thermostats cost less. [5] If you already keep a good schedule, a programmable model gets you much of the benefit.
Will a smart thermostat work with my heat pump?
Only if the model lists heat pump support and matches your stages of auxiliary heat. DOE advises using a thermostat designed for heat pumps before setting back, so backup electric-resistance heat does not switch on. [5]
Do I need a common wire?
Many models do. If your wall has no spare wire, look for the manufacturer’s power adapter or have an HVAC contractor add a wire. Do not force a connection you are unsure about.
Can I install one myself?
Many homeowners do, with the power off and a photo of the old wiring. If the system is line-voltage, has unfamiliar wiring, or involves gas equipment you are unsure about, hire a licensed professional.
Switch off power to the heating and cooling system before touching thermostat wiring, and use a licensed electrician or HVAC contractor for line-voltage circuits, damaged wiring, or anything you cannot identify. Savings figures in this guide are ranges and manufacturer claims, not predictions for your home.
Sources
- Smart Thermostats (Smart Home Tips) | ENERGY STAR. U.S. EPA ENERGY STAR, accessed 2026-10-12
- Smart Thermostats | ENERGY STAR. U.S. EPA ENERGY STAR, accessed 2026-10-12
- Smart Thermostats Key Product Criteria | ENERGY STAR. U.S. EPA ENERGY STAR, accessed 2026-10-12
- Savings from your ecobee | ecobee. ecobee (manufacturer claims), accessed 2026-10-12
- Tips on Saving Money and Energy in Your Home (Energy Saver Guide, 2022). U.S. Department of Energy, accessed 2026-10-12
- Simulation-Driven Rating of Smart Thermostats | LBNL. Lawrence Berkeley National Laboratory, accessed 2026-10-12
- Improve energy savings with your Nest thermostat | Google Nest Help. Google Nest (manufacturer claims), accessed 2026-10-12
Savings, costs and rebate figures are estimates from the dated sources cited on each page; your results depend on your home, climate and utility rates, and incentive programs change often. Gas, venting and electrical work belongs with a licensed professional. This is general information, not financial, tax or legal advice. As an Amazon Associate we earn from qualifying purchases.