While portable boilers for hire, heat buildings and house space, the term space heater is normally used to refer to relatively small heaters for hire, 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. However, a ground source heat pump operating with a coefficient of performance of more than 3 will be cheaper to operate than a gas heater.

Modern electric space heater hire 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 transfer heat to the inside from the outside. The domestic incandescent bulb contributes a small but significant amount of heat to domestic interiors. It is more important in extremely well insulated homes, where such bulbs may be left on so as to extend their life.

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.