How does the 3rd-generation Nest Learning Thermostat save energy?

The Nest Learning Thermostat learns the temperatures that you like when you’re at home and then programs itself. It turns itself down when you’re away. That’s how it saves energy. And here’s the proof.

Most thermostats are programmable. They make you enter every temperature change that you want throughout the day or choose a start and stop time for heating your home. It’s annoying and complicated – many people don’t even bother.

How does learning make a difference?

No more programming. Just turn the Nest Thermostat up and down for the first few days after it’s been installed. It will get to know the temperatures that you like and when you like them. Then it programs itself. It even turns itself down when you’re away so that you’re not heating an empty home. The Nest Thermostat also learns about your home and figures out how it heats or cools, because no two homes are exactly the same. And it considers the outside weather conditions. So, it can figure out when to turn on the heating to get your home to the temperature you want without wasting energy, or when to turn the temperature down to prevent overshooting.

The Nest Thermostat also shows you how to save energy. Each time you adjust your thermostat to an energy-efficient temperature, you’ll see the Nest Leaf. Over time, it becomes harder to get the Leaf, encouraging you to save even more energy. Then you can check your Energy History on the Nest app to see how much you use every day and what has caused any big changes in your energy use. Nest also sends you a monthly Home Report so that you can compare how much energy you’re using this month versus last month. As you learn more about how and why you save energy, you can make simple changes to be more efficient.

How Nest calculates energy savings.

Many thermostat makers claim impressive energy savings, but few disclose the details of how they calculate their numbers. Those who do usually make these assumptions:

  • They assume that customers usually keep their thermostat at the same comfortable temperature, night and day.
  • Then they assume that their customers will program their brand new thermostat efficiently. And keep updating the program over time. So, they assume that the new thermostat will turn up the heating in the morning, down in the afternoon and off in the evening, for example.

We don’t think that’s realistic. Many people don’t keep their thermostat at the same, constant temperature: they change it throughout the day and turn the heating down at night. Also, people very rarely program their thermostats, and it’s even more rare for them to be programmed well.

So here’s what we did to calculate realistic savings:

  • We aggregated data from the Nest Thermostats that have been up and running in real homes across Europe since 2014. We know when Nest turns our customers’ heating up and down, so we have a pretty good idea of how much energy people use with their Nest Thermostats.
  • Next, we needed something to compare it to. In the UK and Ireland, we calculated how much energy people would have used if they kept their homes at 20 ºC all the time and also if some of them turned the heating down to 9º C for seven hours at night.
  • When we compared data from real customers to the estimates above, we got these results:
    UK customers saved 8.4% to 16.5%
    Irish customers saved 9.6% to 18.1%

In a previous white paper for the UK and Ireland, we ended up with a wide range of savings estimates based on different houses, temperatures and schedules, but now that we have real customer data, we can reduce that range and give you more-accurate estimates.