Inline hot water temperature sensor?

Hey Guys-

I’m in the midst of designing a hot water recirculation system for my tankless water heater. I was wondering if anybody knows of a zigbee or z-wave inline temperature sensor that would work with 1/2" or 3/4" pex pipe?

I thought I could leverage my motion sensors to run the recirculation pump, but it would also be nice to know the water temperature at the far end of the recirculation loop in order to decide when to run the system or not.


You might want to try an integrated solutions such as this:

It has a neat feature where a momentary contact switch (eg MIMOlite) can request circulation, but it will only circlulate if the in-pipe temp sensor is below the target temperature.

More info here:

and here:

This looks promising but a bit at the top end of what i have budgeted.

After I posted I found this thread which looks promising.

I’m doing a dedicated return system so I wouldn’t need to rely on the sensor valve.

I’d prefer purpose built sensor similar to what readytemp is using to the home made one rossetyler is using. Do I prefer it to the tune of the $300 or so difference in price? I haven’t decided yet.

Well, unless you figure out that the return pipe is full of hot water in some way, your pump will undoubtedly run longer than you need. The idea of the integrated solution is to run the pump only as long as it takes to get hot water to all of the faucets - and NOT to run the pump if the water is already hot everywhere.

Granted, it’s a bit more expensive to use the redy temp; I’m not trying to sell you, just making sure you understand the implications of both alternatives.

Yeah exactly. I could fake it by timing the pump runtime with a webcore
piston after doing some timing tests, or build a temp sensor as in the
example, which seems like the best bet. What I’m saying is that I won’t
need the one way temp valve to the cold water pipe, since it’s dedicated
return. That seems like the weak point.

Another option is to use an original ST MultiSensor. If you take the guts out of the case, you’ll find the temperature sensor is in a position where you could tape it to the HW pipe in such a way that the sensor is touching the pipe. Although it will read a bit less than the actual water temperature, it does register enough of a rise for you to find an approximate value that you could then use to stop the pump. My app allows use of this sort of arrangement as an option…

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