Netatmo Heat index value for Outdoor module

I have successfully deployed and Netatmo OH2 binding (v 2.1.0). No issues with operations (works perfecly OK for me), but still one simple question to ask:

How is the Heat index calculated/reported? It seems to me showing crazy values and not the expected e.g. according to

Any feedback to my observation would be highly appreciated.




the HeatIndex ist calculated in the binding using the current temperature and rel. humidity. You can see the complete formula here.

May I ask you which unit system do you use in the Netatmo App? Metric or Imperial?


thanks for the reply … I use metric unit system.

just the observation re: the current situation:

Openhab Netatmo Binding measurement
18.0 °C
63 %
Heat Index

Heat Index calculated using the same parameters (18 C and 63%) via is 18 (or 64 using F) … 38 doesn’t fit to any of these figures

I see. Please be aware that this formula is only valid for temperatures equal or greater than 27°C (80°F) and humidity equal or greater than 40% (see

Your link introduces a simple formula for temperatures below 80°F. That could be an appropriate improvement for the calculation in the binding. I double check that.

I see … I’d like to use my Netarmo to connect with Somfy External Venetian Blinds to leverage outside heat index switching them to shade mode and in case of strong wind/gust to make them up.
And in my rule I used 80 (80 F / 27 C + 40% hum) as the heat index threshold parameter for shade scene. I am not meteorology expert, and I would be happy with whatever calculation, which would make more sense.
Anyways, thanks a lot for your support … very much appreciated.

@cweitkamp I just bought Netatmo and bring it to live. Currently i am running OH 2.5M6 and i am a little bit confused with the humixdex and heatindex values.

From my point of view the humidex of 7.2 based on the temperature of 7.8°C and 84% humidty is just fine, but the heat index is about 68.3 °C.

I am aware that the heatindes only work above 27°C and 49% humidity, but what is the binding calculating? Some online services to caclculate the heatindex giving back the current temperature.


My link from second post is broken. Have a look here.

Thanks for the link. This enhanced formula could be found in englisch wikipedia. The problem ist that the formula only work above 27°C & 40% Humidity. Below these values it does not work and that is not refelcted by the function.

I would suggest to change that behaviour. Below these values just the temperature should be returned or somethjing like Nan

Feel free to contribute an improvement for it.

I personally do not think this logic belongs into the Netatmo binding at all. It is kind of business logic out of scope. One can easily implement a similar calculation in a rule - regardless where the input values come from.

During the xmas holidays i will check how to contribute an improvement.

From my point of view a binding should deliver proper values so your so called business logic should be part of the binding. The used formula idicated very clear that values are only valid in a defined range.

Thanks for the link again