I use a heat tape to keep our water meter from freezing in the winter. lining the entire plumbing stack near the meter with the heat tape and then wrapping the whole stack with insulation. Good thing, too, last winter the crawlspace reached 18 degrees F!
I have a DS18B20 probe tied to the copper pipe coming off the water meter and, with the crawlspace temps at 18 degrees the copper pipe reached a temperature of 95 degrees F! Good job insulating, but a bit of overkill on the amount of heat transferred! The heat tape has a thermostat, but that only measures the ambient temp and turns on the heater if the temp falls below 40 F.
Wanting better temperature control (at least not as extreme) and wanting to replace the WiFi monitor I was using (which proved to be unreliable), I've replaced the monitor and added temperature control with my latest Moteino project: The Heat Tape Monitor/Controller (I'm not as clever at naming these things as others on the forum).
This is a relatively simple design using a Moteino, RFM69W, One Wire interface to the temp probe, and a Triac isolator/driver to control the Heat Tape power. I also added a PIC12F1840 for hardware watchdog because I can't afford to have this unit hang up!
I designed this before Felix offered the Proto-PCB, but deciding at the last minute that I really wanted battery backup for monitoring purposes, I added the Proto-PCB with LiPo charger and resistor dividers on both VBat and 5V supplies.
It's all enclosed in a very convenient PolyCase box that has the AC connections built-in.
Attached are photos and the Eagle design files.
Enjoy,
Tom