The 12.5 X 18 size is perfect for most chicks and chickens. Use in the first stages of life for mandatory heat requirements and later when old man winter pays a visit! The internal thermostat is pre-set to the perfect temperature. Ensuring your chicks do not get chilled will help prevent pasting and support a healthy start. Only 40 watts makes the Thermo-Chicken Heated Pad very energy efficient. It can be placed on the floor or mounted to a wall. For use in an enclosure.