Hot Water Tank Temperature

Hi all,

I would like to start monitoring the temperature of the 300L hot water tank that I have, which is connected to the boiler (and has an immersion heater with a SolarEdge diverter).
I couldn’t find much help in the forum on how to do this… Does anyone have any recommendation on what hardware to get (and how to connect it to an emonTx or emonPi)?



Do you have an EmonPi or EmonTX already?

I have an EmonPi, and about to get an EmonTx as I don’t have enough CT inputs

Both will by default accept 6 temperature sensors, but if you have more than one, you’ll also need an expander and Ethernet patch cable.

The sensor needs to be in good thermal contact, so ideally, it should go in a pocket let into the tank wall. If that’s not possible, then depending on how your tank is insulated, you might need to improvise.

I have 8 temp sensors soldered together to a small piece of protoboard and a single cable attatched to an EmonTX screw terminals. Granted the expanders etc are simpler but are more expensive. TIMTOWTDI

If you have more than 6, there’s a small modification required to the sketch. And if that’s the one in the emonPi, there’s a further complication of (a) accessing the sketch and (b) not overwriting it with an update.

As it’s a big tank it would probably have facility for two immersion elements. They’d typically supply with one fitted and then a blank fitted in the other (no. 19 in drawing below). You could possibly get a DS18B20 right into the tank there (although you’d be reading temperature at the bottom – not neccessarily what you want).
tank.pdf (174.7 KB)