[The Atomic Ass]

Originally Posted by Ryland

tempering tanks are most common with on demand hot water as electric on demand hot water heaters have a hard time keeping up with the demand for heat, the draw back to them is that in the heating season you are using that heat in your house to heat the cold water, the energy to heat anything is the same, if it's coming from the warm air in your house, or the heating element in the water heater, that water is still absorbing energy.

Typically the water heater is located in the basement if the house has one, (it does in this case), and basements aren't typically heated unless finished. My parents basement stayed above 60F all winter, despite them using mostly wood heat to keep from running the central.