The ceramic heaters I am familiar with have a ceramic heating element that heats up through resistance. There is a lot of dust, dry litter and feathers/down wafting around inside a coop that will settle on that element. When the heater is on for a fairly lengthy period of time, that debris can heat to combustible levels making it a very good place for the coop fire to start. In short, you won't need to heat the coop so don't. You're heating the coop for yourself, not the chickens as they are hearty enough to get through cold weather without it. A small water heater will be enough to keep the waterer from freezing--either a commercially produced one or one you can, if you're clever, make out of a light bulb. As with any electrical/heating device be very careful how it is set up, what it is touching and make sure it is grounded.