That's the very reason for heating water instead of space, hot water is wanted year-round. It's used for washing both people and things; Swimming pools are nor

That's the very reason for heating water instead of space, hot water is wanted year-round. It's used for washing both people and things; Swimming pools are normally heated, even just a little, above the cold water mains temperature. Hammams need hot water, even in the height of summer. Hot water can be stored, out of the way, in an insulated tank, for when it is required. Instead of providing fully-hot water to a few very nearby households, it can be used as a warm-water input to domestic boilers for a larger number of households over a larger area. Even in a self-contained domestic system, it would be better to pre-heat water going into the boiler, than to just be a radiator that heats the outside in summer.