Thanks! I tried the cookie tin heater and water is still unfrozen this morning, though it only dropped down to -3F or so last night. Still hoping to keep it in the run but may move it inside as you do if it doesn't work outside at really cold temps.
What wattage bulb are you using to keep water from freezing at -18? Is your waterer outside where it's -18 or inside the coop where it's slightly warmer?