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?

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  • How much space do you have round the pipe and p-trap? How cold does it get and for how long?
    – Walker
    Feb 4, 2011 at 16:22
  • I added a photo to demonstrate. I'm down in Texas so we usually don't get more than a few days of freezing weather per year, so I have just been living with it when it happens. However this year has been brutal with whole weeks where it doesn't get above freezing.
    – JohnFx
    Feb 4, 2011 at 16:27
  • You might need heat tape at this point ... but for normal conditions, you might just be able to get away with insulation, if it's only spending short periods below freezing.
    – Joe
    Feb 4, 2011 at 16:31
  • 1
    I just have to ask. Why is that outside? And why don't you reroute it inside (the way it probably should be)?
    – Tester101
    Feb 4, 2011 at 17:48
  • There is nowhere to put it inside, unfortunately. It was this way when I moved in, and I assume it was an add-on after the fact. Also, it is a log home so most of the walls don't have interior space.
    – JohnFx
    Feb 4, 2011 at 18:00

6 Answers 6


I would build a small insulated enclosure around the trap and drain. Could easily be constructed with a couple pieces of lumber or some left over log siding. (see you have log siding on the wall) Heat tape could scorch the PVC and be hard to regulate.

  • 1
    That's not siding. Those are actual logs. It is a log home.
    – JohnFx
    Feb 4, 2011 at 20:35
  • 3
    maybe you can make the drain a little log cabin! Don't forget to chink it. hehe Feb 4, 2011 at 22:01
  • 4
    I second the idea of a small enclosure. When it gets insanely cold - this is something full time RV'ers do... use a trouble light (drop light) with a 40-60w incandescent bulb inside that enclosure to keep the temp above freezing.
    – kkeilman
    Feb 5, 2011 at 5:24

Heat tape will work fine, it doesn't get hot enough to melt things. There are thermostatic ones that are designed for the sole purpose of keeping things from freezing. PVC is rated for a minimum of 140 deg F. and in non-pressure applications like DWV as is your case can probably handle a little higher temperatures than that before they deform.

  • This makes sense to me, why would heat tape get over 100 Nov 4, 2019 at 11:55

We also have a log home that sits 4' feet off the ground (flooding issues) and had the same problem with the shower drain. We just add a cap full of RV antifreeze after showers when we know it might freeze. This seems to stop the problem (when we remember to add it). Now we have a problem with the drain for the boiler that I believe will be fixed better with the heat tape. Wish me luck!

  • 1
    That is a great idea. A little worried about what that might do to the septic though.
    – JohnFx
    Dec 9, 2013 at 21:54

I live in Maine where temps drop -20 during the winter, the trap for the shower was placed under the house in a crawl space, got tired of crawling with my heat gun to thaw the pipe before every shower,I wrapped a heat mat around it connected by a thermostat controlled heavy duty extension cord. solved the problem


water softener salt will do the trick but could take a few days, depending on the depth of the ice dam. A more permanent solution is an internal waste line heating cable and transformer. https://hotlineinternalpipeheater.com/HotLine-Internal-Sewer-Pipe-Heater-Installation-Video-Over-30-feet.php

  • 1
    Hotline internal pipe heater is a more permanent solution to keeping main 4" lines from freezing, especially when you suspect a belly (Low spot) in your main line to septic. Jan 24, 2017 at 21:12

Building a serenaded enclosure insulate with spray from a 2 or 3" hole for a heat duct works grate some small metal screen over the duck insert keeps thr critterers out.

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