There are too many types of heaters to discuss in full, but let’s look at the most common varieties. These days, heaters typically use one of two energy sources: gas or electricity. In the case of gas heaters, the gas is burnt to produce heat; electric heaters, on the other hand, pass an electric current through a resistant conductor, such as a coil of metal wire. The conductor dissipates the energy from the current as heat.
There are two main types of gas heater: vented and unvented. Vented gas heaters have a permanent connection to a flue and are often completely sealed — one duct brings air in from outside, another takes out the exhaust fumes. This is seen as the safest type of gas heater. Unvented gas heaters are intended for outdoor use, since they emit their exhaust fumes directly.
Electric heaters differ in that they produce no exhaust fumes. This means that all of the generated heat can be emitted safely into the room. No heat is lost to a flue, as with gas heaters, meaning the heater is highly energy efficient. There are a few different types of electric heater: Micathermic heaters heat air within a cavity and rely on natural convection to distribute the warm air throughout the room. Ceramic heaters use a hot ceramic disc in combination with a fan to distribute the hot air. Convection heaters work with or without a fan, and use an electric coil within a chamber filled with oil. They can look similar in shape to a central-heating radiator.
Oil-filled convection heaters sell from about 50 USD; micathermic heaters from about 30 USD; and ceramic heaters from about 20 USD.