Farm Innovators 3 gal. Plastic Heated Poultry Fountain HPF-100
Product Review (submitted on January 11, 2014):
Well, now that our "polar vortex" is past, I can definitively say the heater is good to about zero Fahrenheit. At -7 below zero, water in the tray was frozen solid, though the main chamber still had liquid water in it. Design changes needed: heater needs to overlap the outside water tray, better locking system (have had the same problems others have mentioned with getting soaked when it popped open). Didn't know I could fill it through the bottom, may try gluing the lid on like Glyn mentioned. Don't think top filler will work, difficult to maintain vacuum (which is poor as it is, with water syphoning out the bottom if it is not perfectly level). Mediocre design, but the only thing I've found available so far. Have a home-made heater in the barn made from a galvanized pan and a light bulb, but not feasible for the mobile coop.