What a great invention:
The Underwater Wood Stove is nothing short of ingenious: you heat your Snorkel Hot Tub with a wood stove — an underwater wood stove made of marine grade aluminum coated with a corrosion-proof finish for years of trouble-free service. Completely submerged except for air intake, fuel feed, and chimney, the stove transfers heat to the water so efficiently, the underwater portion of the stove stays cool to the touch. The heating efficiency of the Snorkel® and Scuba® Stoves is far greater than outside the tub stoves which depend on thermal convection and with no plumbing there are no concerns of plumbing freezing and bursting. Wood-Fired Hot tub kit from Snorkel.com:
Link: http://snorkel.com/hot-tub-info/snorkel-and-scuba-stoves.php#