Multiple temperature sensors - best way to do it

[Robert.Wall]

@novemberromeo

I have a rather complicated UFH system with various mixers (which probably shouldn’t be there) and buffer tanks. I think there are actually 12 temperatures I’d like to monitor eventually, but for now I’ll start off with 6.

My question is what are the options to go from 6 to 12 sensors? I understand the RJ45 breakout boards can be connected together, so I could wire up 12 to the one pi, but the firmware of the pi is limited to 6 sensors so it wouldn’t actually work. Is this right?

Is this right? - yes and no.
The easy answer to the wiring question is breakout boards aren’t the best idea. With 12 sensors, you will be less likely to run into problems if you daisy-chain the sensors, rather than wiring them all back to a single point in “star” configuration. There’s a little more about this in the ‘Learn’ section, and a lot more in these topics DS18B20 reliability considerations - #7 by pb66 and Ds18b20 and emonTX3CM firmware - post 78 in particular.
Your 4-pair telephone cable should be fine - choose the cores to use based on what PB has written (the first link above).

You don’t mention if you’re using the emonPi for monitoring power. If you are, and you swap to the emonPiCM software, then 12 sensors have never been tested and most probably will not work - because a huge amount of time (comparatively) is taken while each sensor sends its data. If you use software that’s the default today, then with minor changes (which we can steer you through) the emonPi should be OK.

If you are doing power monitoring with your emonPi and need the Continuous Monitoring software, then I’d be sorely tempted to suggest a Raspberry Pi (not even an emonPi or emonBase) dedicated solely to servicing the temperature sensors, and that can sit on your LAN and send the temperatures to the emonPi for logging or whatever. Unfortunately, there’s not as I recall any standard software for the RPi to do that.