I saw this on a Google search and thought I'd try it out. It actually went pretty well. I'll see how it works agter this expected cold front comes through Va tomorrow. It's basically a light socket that plugs into an outdoor extension cord with a 40 watt bulb. I lined the inside of a half cinder block with foil. The block rests on top of a board and I notched out a little spot at the bottom of the block for the cord to fit under. The waterer hangs just above the block, less than an 1/8 of an inch. I'm confident it will provide enough heat to keep the bottom of the waterer from freezing. I'll update after the temps drop.