There are many brands of external heaters available in the marketplace today. Among these, the “Chofu” heater is particularly popular. Chofu and other brands of external heaters most often utilize a process known as “thermal siphoning”. The transfer of heat in thermal siphoning is quite slow, but can be increased by adding on an electric pump. On its own, an external heater will take upwards of two thirds the time to heat a similar amount of water when compared to a submersible stove. External heaters must also be completely drained in the winter (for those who live in cold-winter climates). The big advantage of external heaters is that they do not use up your valuable hot tub space!
The biggest advantage of a submersible heater over an external version is the speed at which water is heated. Simply put, submersible heaters heat water far more effectively. Whereas an external heater loses some of its output into the air around it, the submersible heater’s output goes directly into the water, since it is submerged. There are also two heat exchanger pipes which trap the heat that would normally be lost through the chimney and return it to the water.
Submersible heaters are made of the highest grade marine aluminum. This material is extremely resistant to corrosion, and it contributes to the high-efficiency output of the stove. There are two sections of each submersible stove. The bottom section is kept cool, because the heat is continuously and quickly transferred away into the tub water. The upper section is very hot, but protected by a cedar barrier, ensuring hot-tubbers are kept safe.
Our submersible stove will heat an 85 cubic foot hot tub (six feet diameter and three feet high) in approximately 2.5 hours. This heater takes up approximately one-quarter the space in the hot tub, but there is still ample room for four adults.