While central boilers that heat buildings and houses heat space, the term space heater is normally used to refer to relatively small heaters, especially those that are portable or wall-mounted. These space heaters may use natural gas or propane, but they are most commonly electric. Electric heaters are safer because there is no danger of carbon monoxide poisoning. They are also cheaper to buy. However, they are often far more expensive to operate, because electricity is typically more expensive per unit of heat energy produced than gas or propane.

Modern electric space heaters usually have ceramic heating elements rather than nichrome wires, and are fan-forced with a blower or squirrel-cage fan. These distribute heat much more evenly, and allow them to be encased in plastic, nearly eliminating the chance of burns or fire. Window and wall units, often seen in hotel rooms, are permanent space heaters. These often employ heat pumps, which use reverse-cycle air conditioning to provide heat to the inside rather than the outside.

Propane space heaters are generally one of two types, radiant (infrared) or circulation-type space heaters. Infrared propane space heaters function to heat objects which in turn heats the surrounding air whereas circulation type space heaters heat the air directly using a fan or convection. Additionally, propane space heaters are either vented or unvented. Unvented space heaters are low capacity heaters used to heat living areas but are not allowed in bedrooms, bathrooms or confined spaces due to fire danger and the possible accumulation of flue gases at high levels.

Kerosene heaters were once common, but may easily cause a fire, and must be completely cooled before being refueled.

District heating

In some countries district heating is a major source of space heating. This is especially the case in Scandinavia. District heating systems make it possible to distribute all of the energy for space heating as well as water heating from waste heat from industries, power plants, incinerators, geothermal heating and central solar heating.

 Efficiency

In most areas, fossil fuels are burned to create heat, which is used to boil water and create steam to turn a turbine that turns a generator that produces electricity. The efficiency for the process ranges from about 20 to 60%. Another 5 to 15% is lost in transmission, depending how far the power plant is from the user. Gas heaters on the other hand, use the heat from combustion to directly heat the space through convection, which is much more efficient than electric heating.

In combined heat and power (CHP) plants the energy lost in e.g. turbine driven power plants is utilized for district heating. When space heating is supplied by district heating from CHP plants, the total energy efficiency approaches 100% (and may even exceed 100% based on the lower heating value of the fuel). CHP is a major part of the strategy for energy conservation and global warming prevention in Scandinavia - and increasingly in the rest of Europe.