Solution: ComfortTile Heated Floors
The heat cable exceeded my expectations. The installation was a breeze; easier than I expected.
Tip: Make sure to use all of the included cable strapping to secure the cable. Drill holes with a concrete bit and screw down the strapping with concrete screws. (The Tapcon brand is available at Home Depot).
Once the travertine tile set for a few days I installed the thermostat and set it for 72 degrees. I was pleasantly surprised to learn that I had turned that lower-level bathroom with a very uncomfortably cold floor into the most comfortable room in the house. I would do this again in a heartbeat, especially with top-notch service and advice that my Warmzone rep provided. For my next home, without a doubt I will consult with Warmzone and then budget for radiant floor heat in all the tiled areas.