These days, humans have gotten all fancy-schmancy with their gas and electric water heaters. Heck, some are even using heat pumps to do the work as efficiently as possible. [HowToLou] got back to ...

Designed to use biomass that might otherwise be wasted, such as wood, twigs, or other agricultural ... they can also be used to provide a large amount of hot water to something like an off-grid ...

For the purpose of making a hot tub, any style can suffice. The process of insulating will need to be adjusted if you go with ...