recommendation for smallest Pi for temp monitor

Hi,

Check out the Adafruit website, they list ready-made temperature sensor boards, i.e. three of these could be used:

https://www.adafruit.com/product/1782

The website there has a write-up explaining how to use those sensors with a Pi or an Arduino. Example Arduino:

https://store.arduino.cc/products/uno-r4-minima

For lower power (a tenth of the power in comparison to a Pi), and less to go wrong you may as well use Arduino, it's simpler and will meet the requirements that you mentioned.

Here's a fairly low-power display, and again there's a write-up explaining how to use it with an Arduino:
https://www.adafruit.com/product/772

If you went with Pi, then although the temperature sensors would function, that display won't work, you'd need a lower-voltage display (3.3V logic levels).

Personally I'd probably use a Pi Pico, but for a complete beginner, there's perhaps more help online for the Arduino in this case, since there are the complete write-ups mentioned above.

I think you'd get all this up-and-running on an Arduino with very little difficulty if you went for those specific parts with write-ups (and ask here for help if you get stuck), if your requirements are strictly limited to what was mentioned.

It's worth mentioning your actual end goal (i.e. what the three temperatures are needed for) in case there are more tailored suggestions for your needs. For instance, perhaps logging or charting or wireless monitoring is needed. Also, it's unclear how far away you may wish the display to be. The parts suggestions above assume all parts will be close to each other, i.e. no sensor cable much longer than 60", and the display not much further than a couple of feet from the Arduino too. All the above suggestions go out of the window if you have something much further in mind. And in some circumstances it may be impractical to create this from electronic components for a beginner, and ready-made items could be used, such as off-the-shelf fully enclosed sensors and interfaces such as RS232 or Bluetooth.

An Arduino Nano or the like with LORA wireless communications, ultra low power, simple and very long range, could run of a LIPO for a long time

I used a Pi Pico and DHT style sensors for my last temperature project. 

community.element14.com/.../pi-home-temperature-monitoring-system----episode-562

The Pi Pico can be put to sleep but I found it still used quite a bit of battery. There are ATTiny or ESP32 based boards that have deeper sleep modes.

If you are not expecting the temperatures to change very often then perhaps an EInk display? I've been playing with the LILYGO® TTGO T5 board which has both microcontroller and display and would be quite capable of running 3 temperature sensors off a battery.

curious63 said:

So my question is this: Is a Pi nano appropriate for this? and if not, what would be the best raspberry pi option for the lowest power consumption to accomplish this?

I assume by the question, that you're hoping to use Python as that's what most people use on a Raspberry Pi. However, the issue with almost all single board computers is that the power consumption is quite high. As such for this sort of application you'd typically use a microcontroller, but most microcontrollers are resource limited so Python doesn't cut it. However, there are a few MCU's out there which can work with microPython such as the Raspberry Pi Pico board. Check out the Raspberry Pi Pico documentation to learn more: www.raspberrypi.com/.../micropython.html