It seems that low-tech, wood-fired hot tubs are trendy again. According to the NYT, this could be either due to the fact that old-school hot tubs are cheaper or simply because of a certain nostalgia:
It's fun, like a ritual that you plan hours in advance. You chop the wood, get the firebox going and get really good at managing the fire to keep the water in a narrow range of 104 to 106 degrees. You have a real outdoor experience, as opposed to a Las Vegas experience.
No matter what the reason for this recent trend, you can head over to the NYT to learn more about hot tubs, new and old. [New York Times]