We bought a de-icer for the sheep water tank. The tank is plastic and holds 40 gallons, so we got a floating de-icer from Jeffers which is safe for plastic tanks. The installation instructions emphatically state that extension cords should not be used. This meant we needed an outdoor outlet near enough to the tank to plug the de-icer in, and the cord they provide is *maybe* 6 feet long, but probably more like 5 feet. So, Monday night we ran a new circuit from the barn out through the wall into the sheep shelter, and mounted an outdoor GFCI outlet in a protected area that was close enough to plug into.
This de-icer is the greatest thing since sliced bread. It's a 1250W unit, which is plenty big enough for 40 gallons. The other night the temp went down to 17, and there was absolutely no ice in the tank in the morning. No more breaking slabs of ice out of the tank and freezing my fingers off. Yippee!
It took us all night to finish the installation though. It was snowing like crazy and the sheep were looking at us like we were nuts. We kept invading their shelter, so of course they would go out and stand in the snow, wander over to the hay feeder for a bite, and then come back and wonder when we were finally going to leave so they could come inside and lay down. We finally finished up at 11:30pm. There was 4 inches of snow by then, and the sheep were wearing some of it. It was a real visual lesson on the insulating value of wool. The snow just sat on their backs without melting. They would let it pile up for a bit and then shake it off. I wish I'd gotten some pictures.
The de-icer has a thermostat, so it doesn't run constantly, which is a good thing. It will be interesting to see what the next electric bill looks like!