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Knowledge Base document #3391

Using open window detection for FRITZ! radiator controls

To save energy, the open window detection of the FRITZ! radiator control, for example FRITZ!Smart Thermo 302, closes the radiator valve while the room is being aired out. Open window detection is always active for each individual radiator control, even if you are using a FRITZ! smart plug as an external temperature sensor, for example.

You can also use the door/window contact FRITZ!Smart Control 350 for open window detection in combination with your FRITZ! radiator controls. The radiator control keeps the valve closed as long as the door/window contact signals that the window is 'open'.

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

1 How open window detection works

The open window detection of the radiator control closes the radiator valve when the radiator control measures a temperature drop of 1.1 degrees within 2 minutes. You can increase the sensitivity to 0.7 degrees or reduce it to 1.9 degrees in the FRITZ!Box. In the factory settings, the valve is set to remain closed for 10 minutes. You can set the duration in the FRITZ!Box user interface.
As soon as the valve is closed, the time when open window detection will stop again is then shown on the display of the radiator control, and some models also display a snow crystal symbol.

Due to structural and thermal conditions, the radiator control may not accurately register a decrease in temperature. In this case, you can set different values for the sensitivity of open window detection in the FRITZ!Box. If changing these values does not automatically trigger the function, you can simply manually trigger the open window detection on the radiator control.

If you organized your radiator controls into groups, open window detection is triggered on all of the radiator controls in this group as soon as the function is triggered automatically or manually on one of the radiator controls in the group.

2 Setting sensitivity and ventilation duration

  1. Click on 'Smart Home' in the FRITZ!Box user interface.
  2. Click on 'Devices and Groups' in the 'Smart Home' menu.
  3. Click on the (Edit) button for the radiator control you want to set up the function for.
  4. Under 'Open window detection', set the 'Sensitivity' with which the radiator control should react to temperature drops and trigger open window detection:
    1. Click on 'high' to trigger open window detection when the temperature drops 0.7 degrees.
    2. Click on 'medium' to trigger open window detection when the temperature drops 1.1 degrees.
    3. Click on 'low' to trigger open window detection when the temperature drops 1.9 degrees.
  5. In the 'Valve closed for' field, enter how long in minutes the valve should remain closed. You can enter a value between 1-120 minutes. For example, if you usually air your bathroom for 20 minutes, enter '20'. When this time has elapsed, the radiator control will behave as usual.
  6. Click on 'Apply' to save the settings.

3 Manually triggering open window detection on the radiator control

If the automatic open window detection cannot be triggered automatically due to the existing conditions, you can trigger the open window detection manually:

  1. Push the button (open window detection) or push the button (open window detection) for 2 seconds. Now the valve shuts for the amount of time you configured in the FRITZ!Box.
  2. You can always change the amount of time by pushing the plus or minus button on the radiator control. The amount of time is then shown on the display of the radiator control.
  3. If you want to heat again before this time has elapsed, push the button (open window detection) or the button (open window detection) on the radiator control for 2 seconds to return to the regular schedule or use the boost function.

4 Using a FRITZ! door/window contact for open window detection

You can also use the FRITZ! door/window contact for open window detection. The radiator control keeps the valve closed as long as the door/window contact, for example FRITZ!Smart Control 350, signals that the window is 'open'. The symbol is shown on the display of the radiator control and then the antifreeze function is enabled:

  1. Click on 'Smart Home' in the FRITZ!Box user interface.
  2. Click on 'Devices and Groups' in the 'Smart Home' menu.
  3. Click on the (Edit) button for the door/window contact.
  4. Select the desired radiator control under 'Open window detection for radiator control'.
  5. Click on 'Apply' to save the settings.

To save energy and minimize DECT radiation, FRITZ! radiator controls only communicate with the FRITZ!Box at certain intervals. Therefore, the FRITZ! door/window contact may not notify the radiator control that the door or window was opened until about three minutes later, so the radiator control does not react until then.

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