Learn about True Radiant and how to change settings

True Radiant helps keep homes with in-floor radiant or radiator heating systems more comfortable by helping to reduce temperature swings typical of radiant systems.

With True Radiant, your Nest thermostat can turn heating on early to help your home warm to a scheduled temperature on time, and turn it off early to help prevent overshooting the target temperature. You can set the limit for how early it will turn your system on, or you can turn it off if you prefer to manually control exactly when your system starts and stops heating.

Learn about radiators and radiant heating

Radiant systems heat your home using pipes filled with liquid or electric coils placed under the floor or in the ceiling. Radiator systems send hot water to radiators in each room.

Because these systems can take so long to heat up, it can be difficult to set a temperature schedule that gives you the level of comfort you want on time. For instance, you may need to start heating at 5am to get to the temperature you want at 7am.

Radiant systems can also overshoot your target temperature since the electrical coils or hot water pipes stay hot even after the system has stopped heating. This means your system may no longer be heating, but the coils in each room can continue to raise the temperature.

Traditional On/Off boilers without True Radiant

How True Radiant works

true radiant image With True Radiant, your Nest thermostat learns how long your radiant system
takes to heat up your home. It’ll turn the heat on early to reach the scheduled
temperature, then turn it off early so your home won’t heat over the
temperature you want.

 True Radiant automatically adjusts when the system turns on and off. There’s no need to guess how early you need to turn on the heat to get the temperature you want when you want it.

For example, the Nest thermostat may learn that to reach 21.5ºC, it should turn the system off when the room hits 19ºC because the already hot radiators will take your home the rest of the way to 21.5ºC. The Nest thermostat will also maintain that temperature by turning your system back on before the temperature gets too low.

How True Radiant works with boilers that have On/Off control

With True Radiant, the Nest thermostat learns how long your home takes to heat up. It will turn the heat on early to reach the target temperature, then turn it off early so your home won’t go beyond the temperature you want.

True Radiant will make your radiant system run like it always should have. There’s no need to guess how early you need to turn on the heat to get the temperature you want when you want it. You simply tell your Nest thermostat what temperature you want and when, and True Radiant will take care of the rest.

True radiant use case

On/Off boilers with True Radiant enabled

For example, the Nest thermostat may learn that to reach 20ºC, it should turn the boiler off when the room hits 19.5ºC because the radiators are already hot and will take you the rest of the way to 20ºC. The Nest thermostat will maintain that temperature by turning your system back on before the temperature gets too low.

True Radiant settings and OpenTherm-enabled boilers

There are a couple of key differences to the settings below if your Nest thermostat is connected to an OpenTherm compatible boiler:

  • The maximum preheating duration setting will be 0-2 hours, instead of 0-5 hours.
  • If True Radiant is turned off, 3rd generation Nest thermostats won’t dynamically change the supply temperature for OpenTherm-enabled boilers using modulation. Instead, they will instruct OpenTherm-enabled boilers to start and stop heating based on the temperature that your installer set in the supply field in the Nest thermostat’s Pro Setupmenu.

How True Radiant works with OpenTherm modulating boilers

With True Radiant, a 3rd generation Nest Learning Thermostat that’s controlling an OpenTherm-compatible boiler will use OpenTherm to set the boiler’s target water temperature. The boiler will then modulate according to the Nest thermostat’s setting, using more or less gas as required to meet the set water temperature.

True radiant use case modulating

OpenTherm-compatible boiler with True Radiant enabled

By changing the boiler's target water temperature, the Nest thermostat can keep your home even closer to your desired temperature. This improves both comfort and efficiency because your system can maintain your home's temperature more precisely.

How True Radiant and modulation over OpenTherm can affect system runtimes

If you have a 3rd generation Nest thermostat installed with an OpenTherm compatible boiler, when True Radiant is enabled, you might see long heating times in your Energy History and Home Report. This is expected.

Since your 3rd gen Nest thermostat will tell your OpenTherm compatible boiler how to modulate when True Radiant is enabled, your heat can run for long periods of time – but the heating water will be at a lower temperature to control your home’s temperature more precisely.

Long heating times don’t necessarily mean more energy is being used. In fact, this type of heating control can be a more efficient way to keep you comfortable because your boiler will use an optimal amount of energy to heat your home as needed.

How to change True Radiant settings 

You can enable or disable True Radiant, or change the maximum time it can preheat with Max Duration. Changing True Radiant's Max Duration setting will only affect preheating during the night (specifically after 8pm), since it's designed to keep you from being woken up too early by a noisy system turning on.

True Radiant is enabled automatically when your Nest thermostat is connected to an in-floor radiant or radiator system that circulates hot water for heating.

You won't see this option if you have another type of system, you'll see Early-On instead. But in some rare cases, you may have a heat pump that controls cooling and an in-floor radiant or radiators for heating. If so, you'll see both options and use Early-On to control pre-cooling and True Radiant to control preheating.

You can change True Radiant settings on your thermostat or with the Nest app.

With the Nest thermostat

  • Press the thermostat ring to open the Quick View screen.
  • Select Settings Nest settings icon.
  • Select Nest Sense.
  • Select True Radiant.
  • Choose No to disable it or Yes to enable it.
  • Choose Max Duration to change how early True Radiant will start heating at night.

With the Nest app

  • On the app home screen, tap Settings Nest settings icon.
  • Scroll down and select your thermostat.
  • Tap True Radiant.
  • Tap the switch to enable or disable it.
  • You can also choose Max Duration to limit how early your system can start preheating at night.

How to preheat your home when everyone's away 

Your Nest thermostat will only use True Radiant to turn on your system early when someone is home. If everyone's away and your thermostat is set to Eco Temperatures, it will wait until the first person comes home to start heating. if you use Home/Away Assist, your thermostat will stay in Eco Temperatures while your home is unoccupied.

How to manually preheat your home when you're on the way back

Radiant heating systems are very efficient but they can take a long time to warm your home. So starting to heat your home early is essential to reach your preferred temperature by the time you arrive. There are two options to do this:

  • If you'd like your home to be at a comfortable temperature by the time you arrive, use the Nest app to switch your thermostat from Eco to Heat. This will allow your Nest thermostat to try to heat your home before you arrive.

  • You can also use a solution like Google Now to automatically start heating to the target temperature when you're on the way home.

Was this helpful?
How can we improve it?