Propane is a hydrocarbon fuel that is generally stored as a liquid in pressurized tanks, and can be burned to produce heat. Electric heaters require a strong power source, such as an outlet fed by the main power grid, to supply enough electricity to produce useful heat. For this reason, electric heaters are rarely used in rural and outdoor settings far from the power grid--settings in which a portable fuel supply gives propane and similar heaters a distinct usability advantage.
Since before recorded history, humans have used hydrocarbon-based fuels, like wood and coal, as a source of fuel and heat. More modern fuels such as oil, natural gas and propane are continuations of this paradigm, but can be controlled in more precise ways to allow for finely-tuned heat distribution and use by indoor furnaces and digital climate-control systems.
Like all hydrocarbon fuels, the improper burning of propane indoors can produce fatal levels of carbon monoxide gas.
Resistive Electric Heating
Typical electric heaters operate on the principle of electrical resistance. Electric current enters the heater from the wall outlet and is passed through a filament. The heater's filaments resist the electric flow and become hot as a result, then release their heat to the surrounding area, sometimes with the assistance of a fan.
Electric Heat Pumps
A variation on electric heating is the modern heat pump. Made possible by the invention of refrigerant chemicals like Freon, heat pumps use an electric pump and compressor to force the refrigerant to cyclically change phase from gas to liquid, and thereby absorb and release heat. Most heat pumps also use fans to force the building's air past the heated coils and then blow it through vents back into the rooms.
Heat pumps tend to work most efficiently at temperatures above freezing.
Modern Propane Heat
Propane has become very popular as a portable heating source for outdoorsmen, campers and others who spend time in settings away from electric power sources. Propane's high energy content--over 21,000 BTUs per pound--and ready portability in handheld and larger tanks makes it a good option for settings where weight is at a premium.
Companies such as Rinnai and Hamilton also make indoor propane furnaces that work similarly to natural gas furnaces in heating a home or living space while venting exhaust gases outdoors.
For all years since 2000, U.S. Energy Department statistics show propane costing substantially less than electricity per unit of heat.
Forced-Air Propane Heaters
Some manufacturers have merged propane and electric heating into innovative portable and semi-portable forced-air propane heaters. Often used outdoors in winter, these systems use an electric fan to direct the hot air produced by a propane burner toward people or spaces in need of heat. Because of propane's high energy content, these heaters provide more heat more economically than electric heating could provide alone.
Modern Electric Heat
Even smaller portable electric heaters often require at least 1,000 to 1,500 watts of power to effectively heat a small space, meaning that a generator or grid-powered outlet is usually necessary to use them. This makes them useful indoors, and in other settings where propane burners present an unacceptable risk of fire or CO poisoning. Resistive electric heaters can become expensive to run, particularly depending upon local electric rates.
An advantage of resistive electric heaters is that they're simple to use and move, and don't require the handling of flammable fuels.