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 Google 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.

Differences between radiant and forced air heating 

Most conventional heating systems send warm air through vents, these are called forced air systems. These systems can change the temperature in your home quickly. Radiant systems generally take much longer to heat and cool down your home.

Instead of heating air, 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.

radiant forced air graph

How True Radiant Works 

true radiant image Although radiant systems work very differently than forced air systems, most
thermostats treat them the same. The Nest thermostat's True Radiant treats
radiant systems differently by automatically adjusting 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.

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.

For example, the Nest thermostat may learn that to reach 71°F/21.5°C, it should turn the system off when the room hits 69°F/19°C because the already hot radiators will take your home the rest of the way to 71°F/21.5°C. The nest thermostat will also maintain that temperature by turning your system back on before the temperature gets too low.

true radiant graph

With our improved learning algorithms, the Nest thermostat can be more precise with how it controls your system depending on the current weather, what the forecast is for the next few hours, and how warm it is in your home.

This helps your thermostat ensure it meets your scheduled temperature on time, maximizes energy savings, and maintains the temperature you set, even with in-floor radiant systems that are very efficient but that are also slow to warm up.

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.

Troubleshooting when True Radiant settings are missing 

Nest thermostats detect what wires you have inserted into the connectors to tell what kind of heating and cooling system you have.

If you don't see True Radiant settings on your Nest thermostat or in the app:

  • You may have a non-radiant system (like forced air)
  • You may have picked the wrong system type during thermostat setup
  • There may be a wiring issue that makes your Nest thermostat think you have a non-radiant system

To troubleshoot, first check what kind of system you have installed, then check your thermostat's wiring:

  1. Check your system type
    If your system blows air through vents in your home, you have a forced air system. True Radiant doesn't work with forced air systems. They use Early-On instead to manage preconditioning.

  2. Check your Nest thermostat's wiring
    Pull off the thermostat's display and confirm it's wired correctly. Use the Nest thermostat wiring diagram and the picture you took of the wires in your old thermostat as a reference.

  3. Check your heating type
    On your thermostat, go to Settings Nest settings icon and then Equipment and then Heat Type. Make sure to select the correct type of heating system: Forced AirIn-floor Radiant, or Radiators. Choosing Forced Air will hide True Radiant as an option in the Nest Sense menu and enable Early-On instead.

    Note: If you have both radiant heating and a cooling system, you may see True Radiand and Early-On options in the Nest Sense menu. True Radiant will control how early your home preheats and Early-On will control how early your system pre-cools.

  4. Get a pro to help
    If you can't figure out your thermostat's wiring or the settings, contact a local Nest pro to help.

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