For a relatively small price, you can build this hot tub in ... we used a wood-fired thermosyphon heat exchanger. This 3/4-in. stainless steel coil circulates the water without a pump.

Heck, some are even using heat pumps to do the work as efficiently as possible. [HowToLou] got back to basics instead, with his simple wood-fired water ... re looking for a hot shower from your ...