A friend had an addition built that is 2 feet or so off the ground.
There is a tub in it on the outside wall. So the drain runs back to
the house in the "floor". When it gets really cold, the (metal) drain
freezes at the P-trap. This can be avoided by pouring a little
windshield washer fluid in the drain at night, but the tenants who rent
the place often forget.
Of course the drain pipe has lots of pink stuff around it but that just
minizes heat loss. It doesn't generate any heat though. We cut a hole
in the base of the tub enclosure to permit warm air to circulate around
the drain pipe, but it didn't help when the temp went down to -15 F
Thanks for the suggestion.
There are several problems with using heat cable. First, to access the
pipe means ripping apart the bottom of the addition floor. It can be
done but we hope to find a different solution. Second, those cables
use a lot of juice, even with a thermostat. The one I used last
January was 500 watts. It worked but the electric company started
reading my meter in RPM. Third, I am concerned about a possible fire
hazard having a heat source in a confined space with no air flow.
* Heat tape, (The usual answer)
* Build a foam box around it, and hang a 100-watt bulb
off the trap (what I did in my house)
*Build the same box, but skip the heat-tape, fill it with
great-stuff, and hope that that's enough t keep it from freezing.
* Dig a three foot deep trench under the house, and bury
the the drain and trap below the frost-line. (A bit late for that)
* Take the P-trap out, and re-route the drain and vent to the main
basement, and stick a P-trap THERE, illegally far from the tub.
(This will probably smell bad, since you'll have 8' of pipe before
the water-seal, but it will work)
* Design and install an automatic anti-freeze dispenser.
(Creative, but expensive).
* Refuse to fix it for an extra day, every time the thing freezes,
until the tenants figure out to add antifreeze every time.
Those are your options.
Why do you have to rip up the floor? Is there no access hatch to the crawl
space? If not make one . Then there is also access for any other future
problems . Then insulate the perimeter of the foundation. That should help
insulate the floor of the entire addition as well. a short length of heat tape
around the P shouldn't run up the bill too much. Less likelyhood of fire with
the tape than a light bulb or heat lamp.
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