The p-trap for a drainage line (PVC) from one of my showers happens to be outside the house in an area that isn't protected from the cold/wind (yeah, I know) so when it freezes outside the water in the trap tends to block the drainage and back up water into the shower. I am considering installing thermostatically controlled heat tape to the pipe during the winter to the U part of the pipe to prevent this.
My Question: I'm a little concerned about the risk of melting the PVC pipe, especially since it won't typically have running water going through it to dissipate the heat. Also, the shortest heat tape I could find was 3' which is probably going to mean some of the tape is going to run past the part of the trap that will actually have water in it.
I'm considering heat tape with a thermostat, so in theory it should cut off before it does any damage, but I just wanted to check with the home improvement experts to see if that application is a good idea, or if you guys have alternate suggestions.
So what do you think? Will this work out and do you have any suggestions for how to use heat tape correctly in this scenario?