Zone heaters are heaters that are used to heat certain spaces or rooms often referred to as 'zones.' Zone heaters come in a variety of designs and technologies, including ductless split wall-mounted units and smaller portable radiant or infrared heaters. Unlike central heating systems, zone heaters concentrate heat to smaller areas, usually where the family spends the most time. It's not unusual for a home to have more than one zone heater. The purpose of zone heaters is to reduce the home's heating expense and make some areas more comfortable, while those spaces not being used, remain cool. Except for ductless split systems which must be installed, portability is generally the key feature of a zone or room heater, so it can be relocated to a different zone or area as needed.
As for energy efficiency, the energy savings will vary from one home to another depending on the type of technology and efficiency of the zone heater, how long it is used, how well the home is insulated and climate conditions. But some savings should be realized when one zone or room is kept comfortable and the main heating system is turned down for the rest of the home. There are many different types of zone heaters available, and they tend to vary considerably in price and capacity from $20 to several hundreds of dollars. For best results, size a heater's capacity to the main room you want to heat.