Hot callus pipe DIY- what concept am I missing?

Inspired by all the positive comments re: hot callus pipe, dating back to 2016, I thought I’d give it a try. However, I think I’m missing a key concept. The automatic electric water pipe heating cable I purchased is supposedly able to heat up to 100F, triggered by its own thermostat intended to keep water above freezing. It would not come on in a greenhouse at 50F. Makes sense.
I then assumed that all who wrote about this method intended to use a separate thermostat so I hooked the heating cable to my Pymeter thermostat where I could set the max and min temps. But the Pymeter thermostat would not override the cable. It should, shouldn’t it?
To rule out the Pymeter thermostat being defective, I hooked the Pymeter to a lightbulb and was able to control the on and off of light using the heat from lightbulb. Is there some concept I am missing here? Why would the Pymeter not override the water pipe cable?
Finally I switched to a reptile heating cable with no thermostat. OK! Works great! Scions kept at 76F in a 50F ghouse.
Was I missing a step with the water pipe cable?

1 Like

From what I recall, those pre-made cables don’t turn on unless the temp is below 40. The idea is that it won’t spend electricity to protect your pipe unless there’s actually a danger.

Yes, makes sense. But my question is are after-market thermostats designed to override built-in thermostats? For example, using an after-market thermostat to override a refrigerator’s internal thermostat… you can store apples and pears at 34F. Seems like people do this. But it didn’t seem to work on the water pipe cable.

I’ve heard of people doing this with chest freezers to make them cold storage for apples, but that means that it is set to cut off when it gets to 34 degrees. I think that works since the normal thermostat wouldn’t cut off until much lower. But when you wan to use it to make something hotter than it would, it won’t work since the built-in thermostat will activate before you get to the level set by the external thermostat.

When I started using the callus pipe I made, I put in a thermostat to keep it from getting too hot, but then it turned out the pipe never really got over 80ish where I had it set up soil so it never hit the 87 I set the thermostat. I took the thermostat out then and just plugged the heating cable in directly. I’m not sure if it was the cable regulating itself of just that I had enough leakage from the pipe that it couldn’t run hotter even running full time - either way my external thermostat to cut it off if it was too hot was never triggered.

I hope that makes sense.

1 Like

Think of it this way: you’ve got two on/off switches in line, which are set to turn off when the temp is above a certain point. Whichever one turns off at a lower temp wins, unless it gets stuck in the ‘on’ position. With a fridge or freezer, the switch turns on when it gets too hot, rather than off. When you override a fridge with a plug-in thermostat, you’re cutting power at the outlet at a higher temperature, so it’s basically the reverse of the heating cable setup.

which one did you buy? Some are intermittent, some are constant.

Thank you all for your explanations!!

Thanks, that’s it!!

OK got it.

The Frost King Water Pipe Heat Cable I was using must be intermittent.