emonTH 2 with external sensor - recommended location

Just bought a couple of emonTH V2, one with external sensor.
I want to capture temperature outdoor, and before I start drilling holes in walls, I would like to check whether there are any recommendations with regards to:

  • whether the sensor can be exposed to the elements or needs to be protected in some way from rain / sun
  • whether it is better to have it in a shaded area or maybe it doesn’t matter?


Hi Fabre,

You’ll definitely want the sensor in the shade. If it’s exposed to the sun, it will report the temperature as being much higher than it actually is.

This thread has info on how to keep that from happening. The thread deals with humidity sensors, but the info is applcable to temperature sensors as well.

I did see that thread, but it seemed to relate to units that were completely outdoors (emonTX or emonTH). In my case, I was just thinking of drilling a hole through the wall, have the emonTH unit inside, and just the external sensor sticking out of the wall outside (with some silicone sealant).
Do I still need to have a full weatherproof box to protect that sensor?

No prolem there. That’ll work fine.

Not a weatherproof box, but a radiation shield. Preferably, with a fan.

Like this one:

You might want to read the entire thread, as the info is somewhat scattered about.

Those look quite expensive, and I can’t really justify this at the moment…
Out of interest, if I were to install the external probe in the way describe previously (through a wall, in a shaded area, maybe under the roof eaves or external overhang to avoid the worse of the rain), but without one of these shields, how would it affect readings and life expectancy of the probe?

A friend on the west coast of Scotland had a window on a north-facing wall. He drilled through the frame on the east side (so shielded from the morning sun, and the rest of the house shielded it from the evening sun) and that had been working for about 4 years when he left it behind when he moved out early this year. The sensor is inside a stainless steel case, so the vulnerable part is the encapsulation where the cable exits - and that was buried in the woodwork.

There are video clips on youtube that show how you can make one fairly inexpensively.

That’s the next best choice.

The temperature probe needs to be north facing and in the shade.
I have two at home, the first one I installed on the north side of the chimney breast but it suffers from being artificially increased temperatures when the sun is shining due to the ambient heat from the solar panels.
My second attempt was the north facing shed at the bottom of the garden and it works perfectly.
IMHO best way to install external temperature probes is to use an adaptable box with a 20mm stuffing gland to seal everything up, I however managed to find some unused trend boxes.


As long as the box is ventilated - preferably with a fan, it should be OK. Otherwise the readings tend to be artificially inflated.

All of the temp sensors I maintained while an ET for the National Weather Service were in aspirated enclosures.