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OpenTherm and what Nest thermostats can do with it

OpenTherm is a language that compatible thermostats and heating systems can use to talk to each other, enabling thermostats to control heating and domestic hot water systems. The following Google Nest thermostats support OpenTherm:
  • Nest Thermostat E
  • 3rd gen Nest Learning Thermostat

Learn how to tell which Nest thermostat model you have. 

With OpenTherm, the Nest thermostats listed above can control both your boiler’s domestic hot water temperature, as well as the temperature of the water used to heat your home. This is important because many older boilers that don’t support OpenTherm have simple on or off controls. When they're on, they will always heat the water used to warm your home to the same preset temperature, which isn’t always the most efficient way to keep you comfortable.

However, newer boilers allow thermostats to tell them when to adjust their heating water temperature and how high to set it. The boiler will use more or less gas, as appropriate, to reach the water temperature set by the thermostat.

Since your Nest thermostat will tell your OpenTherm compatible boiler how to modulate when True Radiant is enabled, your heat may run for long periods of time but the water used for heating will be set to a lower temperature. This lets your heating system control your home’s temperature more precisely. Longer heating times don’t necessarily mean more energy is being used. In fact, this type of heating control can be more efficient overall.

It’s like when you’re driving on the highway. Most of the time, you’ll keep your car cruising at a regular speed to get you where you need to go comfortably and on time. But sometimes you might need to quickly speed up to get around a slower car or to avoid a hazard.

Modulating boilers work in a similar way: they can use more or less gas when it’s appropriate, to be more efficient while keeping you comfortable. But something needs to tell the boiler what to do. In this case, the Nest thermostat is the one driving. It will use its advanced algorithms to tell your boiler when to change its target water temperature so that it will use more or less gas as needed.

How Nest thermostats make modulation better with OpenTherm

In Europe, the Nest thermostats listed at the top of the page use OpenTherm to control modulating boilers. The Nest thermostat’s learning capabilities and advanced software algorithms like Auto-Schedule and True Radiant, ​account for things like home occupancy, current weather, temperature inside your home, temperature you’ve set and more to control your modulating boiler. For instance, in cooler weather the Nest thermostat can start heating a bit earlier to reach your scheduled target temperature on time.

How to set up OpenTherm heating with the Nest thermostat

There are a couple of things to consider during installation so that your Nest thermostat and OpenTherm-compatible heating system can be set up to work together properly. You’ll need to have a couple of additional wires installed to the Nest thermostat’s Heat Link. If you’re replacing a wired OpenTherm thermostat, you can reuse the existing OpenTherm signal wires with your Nest thermostat. But you should only do this if you have to.

To get the most out of your Nest thermostat and OpenTherm, you’ll need to have your thermostat wirelessly connected to the Heat Link. This is different from connecting your thermostat to your home’s Wi-Fi, but it’s all part of the normal setup process.

Important: The Heat Link is connected to your heating system with high voltage electrical wires. If you have a 3rd gen Nest Learning Thermostat, it should be installed by a professional.

Learn about Heat Link.

How will I know if my heating system is OpenTherm compatible?

One simple way to tell if your heating system is OpenTherm compatible is
to look for the OpenTherm logo (shown to the right) on your boiler or on
your thermostat. The Nest thermostats listed at the top of this article are
OpenTherm compatible, so they also have the OpenTherm logo on their
Opentherm logo

If your boiler isn’t easily accessible or you can’t find the OpenTherm logo, this doesn’t mean that your boiler isn’t compatible. Contact your heating system’s manufacturer and ask about your model to make sure.

If you still don’t know whether or not your system is OpenTherm compatible, check with a Nest Pro.

In the Netherlands, some boilers aren’t OpenTherm compatible out of the box, but they might work with an OpenTherm adapter. Many thermostats use OpenTherm adapters, so your boiler may already have one installed. If so, a Nest Pro will be able to use it with the Nest thermostat. A Nest Pro will also be able to tell you if your system will need an adapter and they can tell you about any additional cost for installation.

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