An immersion heater is used to heat water for purposes such as bathing or showering. The amount of hot water produced depends on how long the heater is switched on for.
No it is not expensive
Depends on the waatage of the immersion heater. Read the name plate details of the heater - it shows the wattage of the heater. Assuming the wattage is 1KW (1000Watt) the KHW will be 1KHW if you use the heater for 1 hour.
If you mean an immersion heater for making hot water, they use 3 kW usually so you get enough for a bath in about two hours.
We do not have a need for a space heater so I have not used one in the past. I would not use kerosene but I would use electric if necessary. Dyson has one that is pretty cool looking.
Full immersion is the best way to learn a language.
A block heater is a device one would use to heat the engine of a car in extremely cold weather. The block heater can be mains generated or will run on the fuel source of your vehicle.
A ceiling fan heater is a type of heater which works in the same way as a standard ceiling fan, but with a heating component. A person may want to use this type of heater if the room does not have access to central heat or any other heat source. An individual may also want to use this type of heater if there is not enough floor space for a standard room heater.
The question is better defined as "What the most energy efficient portable heater?" Because one would assume that you will want to be able to take the heater with you when or if you move.
If one's home is already heated, one can use a ceramic infrared heater for maintaining the heat. The ceramic infrared heater prevents the temperature of the room from dropping.
Most people would want the spa hotter, so in that case there is no way to use only one heater.
The paraffin heater is gas powered. It is not a very safe heater to use as time has proven that they are very dangerous and can overheat or even explode in some circumstances.
A pond heater is used to keep your pond from freezing solid in the winter. A frozen solid pond is bad for your pool liners, koi, and for some pool structures that may use cement.