A Tale Of Domestic Hot Water and a Secondary Combustion Wood Stove.
This is a follow up to yesterday's stove maintenance post, adding explanation of how we heat our water.
A stainless steel water loop inside the woodstove circulates water via thermal siphon (works alone, no pump needed) to and from the stainless tank located beside the stove. Once the water inside the tank reaches a high temperature set point, a sensor turns on a small circulating pump and feeds water to a second tank. Once the second tank reaches a temperature set point, a sensor turns on another pump that circulates the heated water to a third tank.
This third tank has electric heating elements and can be used to top off the temperature before the water is used for domestic use. Last in line is a tankless propane boiler. The electric tank is normally turned off (or turned on during high solar electric days) and used as preheated storage that feeds the boiler. The boiler can then top off the water before feeding domestic hot water needs of the house.
When hot water is used, fresh make up water feeds the bottom of the stainless tank, and the process starts all over. This system pretty much provides an endless supply of hot water.
An interesting side note: the pump controllers in the system are programed as cooling units. Once a high temperature set point is reached at any given tank, the controller(s) think the system needs cooled and turns on the circulator pump(s). The pump runs circulating water from tank to tank to tank, until the temperature falls to the controller's low set point, and turns the pump(s) off.