Joan is right, the pipe heating cable just won't work. I've looked into it as well. However, if you live in the right area you might find a hardware store selling heating cables used for preventing ice from forming in your gutters. It's usually no shorter than 30 ft. for starters but most of the time it has no thermostat although you can usually find thermostats sold with them. I priced it out as well at the Home Depots here in Chicago - the 30 ft cable was about $30. Not bad, but then I started looking at the ZooMed Heat Rope cable and found that due to the shorter lengths it was a better buy for my purposes. I currently run the heat rope down the back corner of three snake racks/caging units I have. I works pretty well to keep a roughly mid 80s hot spot on the one side of the cage.
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Matt Campbell
Animal Keeper, Small Mammal/Reptile House
Lincoln Park Zoo Chicago, Illinois
Assistant Curator
Wildlife Discovery Center at Elawa Farm
Lake Forest, Illinois