Connecting a DS18B20 heat sensor to a modern unvented hot water cylinder

I’m hoping to get a EmonTX (when available) and get some monitoring of my hot tank via a couple of heat sensors.

The tank we have is a modern unvented stainless steel cylinder. That is, the outside of it is a metal casing, there’s no exposed blue foam. My guess is that there is foam underneath, with then an inner cylinder, but I’ve no idea. At a guess you would have to drill through the outer casing, cut back the foam and then somehow attach the end of the heat probe to the surface of the cylinder, some sort of heat transfer glue? I’m not really sure I want to go drilling into the surface of the casing though without knowing what’s underneath.

Anyone got any experience of connecting a heat sensor to one of these? Or any links to anything where someone has done that?


The outer metal casing is just a very thin metal sheet, then there will be foam insulation then the main solid stainless cylinder. Here’s a photo of my tank with the immersion stat cover removed:

It’s no problem to drill a hole in the outer casing them remove some of the foam to attach a sensor. However, most tanks have a dedicated temperature sensor pocket, some tanks have several. Mine is actually marked with a label ‘sensor’!

If you don’t want to drill any holes then attaching the sensor to the outlet pipe will give you a decent reading for the top of the tank and attaching a sensor to the coil inlet or PRV will give you a decent reading of the middle of the tank.

What make and model is your tank? Maybe we can get up a datasheet?

OK, thanks, that’s useful.
The tank is a Daikin tank. There are no built in sensor pockets.
The area under the immersion panel is largely plastic, but there is some exposed tank wall. The temperature sensor for the heat pump appears to just be pushed under the insulation as far as I can see, so I’ll probably do the same. I’ll then probably attach another sensor to the outlet pipe at the top.