As Judy stated, just for your own knowledge, I would use a thermometer, preferably a tempgun, to measure temps on the heat tape itself while the probe is in the tub. My bet would be that the heat tape may be in the 110 to 115 degree range. If that is the case, you are sitting on a fire waiting to happen. I don't recall what size heat tape you are using, but with ambient temps so low, I would suggest moving up to some 11" flexwatt.