Panel heaters are usually compact in size and wall mounted, and can either be used as a simple solution to provide localised heating for short periods in areas such as bedrooms or conservatories or alternatively to provide whole-house heating. Panel heaters have a thermostat to control the room temperature, and often have a 24 hour or 7 day timer. Some models are designed to be linked together and controlled by a central programmer. these heaters are not fitted with thermostats or timers and should only be used in conjunction with an external controller.