Being that type of guy, I enjoy keeping track of the gas furnace’s behavior and the least invasive method is monitoring the inlet and outlet water temperatures. I already have an Ambient Weather station for other things, including a pair of WH31P temperature sensor probes for the heat pump’s outdoor exhaust air and indoor duct temperature. Unfortunately, those sensors top out at (an undocumented in the description) 140 °F and the furnace water runs around 180 °F.
Because I’m more interested in furnace run time than exact water temperature, putting the sensor somewhere between the 180 °F pipe and the 60 °F basement air seemed reasonable.
A quick test showed it might work:
That’s a random cart coin for insulation under a random heatsink for cooling, with the WH31P probe clamped under a snippet of closed-cell packing foam.
Emboldened by 180 °F water in the pipe producing 80 °F at the probe, I conjured a more formal mount from the vasty digital deep:
Which looks pretty much like that in real life:
A layer of heatsink tape holds it to the plastic block, which in turn just sits on the rather crusty pipe surface. The blue wire is a thermocouple reporting the actual pipe temperature and, if the sensor isn’t getting enough heat, a blob of heatsink grease on the pipe will surely help.
The spring arms originally held the heatsink to a PCB atop a Northbridge chip (or some such), so those solderless connectors crimped on shock cord should make it feel at home.
Installing the sensors immediately raised the outdoor temperature by 20 °F at the beginning of an atypically warm November week, so it’ll be a while before I have any results.
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