I don't have one, and had considered making one. I found some great instructions to make one that's homemade. What I decided to do that has worked like a champ is to use an old crockpot. Yes....an old crockpot to keep my chickens water warm / room temp in these winter months. It's awesome and has worked beautifully!! Hope you find something that works for you. I wasn't willing nor could I afford the chunck of change required for a water heater.
Um,yah good concept..bad approach....CHEAP,yes..SAFE dont think so... This needs some safety steps added and a few things changed...He didn't us a out door extension cord and the wood could catch on fire not to mention they could knock over the water container...SCARY!!!!