We use the sun, as well as heat from our wood-fired masonry stove, to heat our hot water. To best take advantage of these renewable heating resources, we invested in a 120 gallon hot water storage tank. Typically such tanks, which are made of cement and fiber, come wrapped with thick plastic insulation. We specifically requested an un-insulated storage tank to avoid the use of plastics and its fumes. Instead, we wrapped natural cotton insulation around the tank. This was probably unnecessary as when a leak forced us to replace our hot water tank, we installed a commercially insulated tank and found that the fumes from the insulation were negligible; however a severely chemically sensitive person might want to know that the un-insulated tank is still an option.
Our hot water is first heated by solar hot water panels on the roof. A closed loop of propylene glycol—a non-toxic, food-grade anti-freeze that can withstand exposure during the cold winter months—is heated in the panels and then travels to the storage tank on the second floor, where heat is transferred to the tank’s water. We are able to use this heating system almost year-round, as the snow very quickly slides from the panels (we’ve noticed that the panels will be free of snow long before the rest of the roof is).
During the winter months, we also use our masonry stove to heat our hot water. When the heater is in use, water from the hot water storage tank makes a loop through the masonry heater. This thermodynamic system functions only when the masonry heater is hot, and no electricity or pump is required for the action.
Finally, as a backup, we have a propane-fueled hot water heater to be used whenever the stored hot water is less than 120° or whatever temperature we choose. This generally occurs only on warmer, cloudy days, when our solar panels aren’t providing heat and our masonry stove is not in use. In our experience with tankless hot water heaters, we have found scalding to be a problem, since the temperature of water passing through the heater’s open flame cannot be controlled so precisely. To avoid this problem, we have the heated water pass back into the tank, and then draw out hot water from the tank itself. In 2008 we replaced our old tankless hot water heater with a Munchkin boiler made by Badedas and three new solar hot water panels on our new slate roof. The system used in our home is being replicated in the new building where our old solar hot water panels have been mounted on the south-facing wall of the carport.