Heating Cables

I saw some cheap heating cables advertised in Ward's Biology Catalog 
(1-800-962-2660) - for those of you who are interested.  The 1992 price for 
them was $25.15.  The catalog description says " Soil Heating Cable. 
 Provides convenient, dependable bottom heat . Ideal for trays, flats and 
hotbeds.  Thoroughly insulated against water and thermostatically controlled 
to turn on whenever soil temperature drops below 74 degrees F.  Thermostat 
can be turned off when bottom heat is not desired.  Has 1.5 meter (5 ft.) 
cold lead, and 3.7 m (12 ft.) cable.  Serves 0.28 square meters (3 sq. ft.) 
bed area. 120 V, AC, 42 watts."   I'm not sure if this is useful for 
aquarium purposes, but I thought I'd pass on the info.