The most common heating methods of a spa are electricity and gas, although there are rare methods like burners and wood furnaces. Technology has brought with it a variety of ways of doing the same thing and the difference is probably in the class of the person using each and every method. The water that is used in the spa has to be heated and this is an added expense as all of it is heated. The method that is employed for heating is related to the size of the spa that is being serviced. There are also heaters that use solar energy, propane gas as well oil for heating.
The most common heating alternatives for a luxury spa and hot tubs are LPG which is liquefied petroleum gas and natural gas. The reason why gas is the most effective heating method is because gas has the ease of regulating because heating is achieved by setting the desired temperature in advance according to your needs. If you use natural gas to fuel a heater, then you will realize that it is the fastest and water heated this way gets hot in a few minutes.
This is by far a fraction of the time it takes an electric heater to fire up and heat up the water. The economies of scale involved with heating large masses of water are what dictate the heating method that is going to be used. For a method that offers lower than usual lower costs, minimal to no maintenance need and instant availability, natural gas is widely preferred to the other methods.
When you use heating oil for spa heating, then it means you need to pay a bit more. If you are using a heater hat is fueled by propane, this is a gas that would easily turn a room into a remnant of soot if not handled with care. This is due to the fact that propane is heavier than air and cannot disperse very quickly.
Using electricity to heat water in a spa is often taken as a standalone project in which there is water flowing into a filter from a pump and then it is heated by the heating element. The normal appearance of commercial and industrial heaters is that they are enclosed in a cabinet which is not the case for luxury type of heaters. You can work closely with home improvement companies to advise you on the best option for your spa.
Spa image by Wikimedia Commons