It seems like I've written about 10 post on threads concerning heating waterers using these with the simple warning: do not use. So I'll make a single thread and hope those with the same questions will read it. I spent 30 year in the aquarium hobby not only as a hobbyist/breeder but I used to write consumer testing reports for a national magazine on a variety of aquarium products, including heaters. In that time I used and checked not only the simple, hang-on-the back of the tank heaters but submersible types made of glass, metal, even heating pad types. Most had the thermostat inside the same tube as the heater but for some units the two were separate. All were designed to heat water from interior room temperature to a maximum of 85 degrees and most weren't total reliable. (Over the years I probably lost more fish from failed heaters--either too hot or too cold--than any other single cause.) The thermostats of most were bi-metal ones that would either stick open or fail to close--just adjusting them often took several days. Additionally, if the water level fell below the heating element when the temperature was below the set one, the heater would not shut off until it either burned out or, in those cases where the tube was glass, shattered the tube. Often when the latter happened the electrical circuit remained open pumping power through the water. In short, they are not made for nor do you want these things in the waterer that is in your chicken coop! There are heaters designed for this thing, either submersible birdbath heaters which are probably okay in areas where the temperatures aren't extreme to specific chicken waterer devices. Don't try elaborate schemes to save a couple of bucks by using an aquarium heater, go with a device designed for the correct job. Chances are you'll end up with one eventually anyway.