I stumbled across this set up when looking for different types of water heaters:
http://hoofinitnorth.com/poultryh2oheater.htm
I figure that is what I am going to try. I am going to do the A/C electric hook up method because we are lucky enough to have electric at the coop. And I am going to use one of the thermostat style plugs for the set up. The neat thing is they have the instructions to do a D/C battery style hook up also. I don't know how well it would work though. You would have to have two car batteries and a battery charger and then rotate the batteries. But it might be a good thing to have as a "just in case" set up.
http://hoofinitnorth.com/poultryh2oheater.htm
I figure that is what I am going to try. I am going to do the A/C electric hook up method because we are lucky enough to have electric at the coop. And I am going to use one of the thermostat style plugs for the set up. The neat thing is they have the instructions to do a D/C battery style hook up also. I don't know how well it would work though. You would have to have two car batteries and a battery charger and then rotate the batteries. But it might be a good thing to have as a "just in case" set up.