It's just that the emissions are moved to a bulk generator as opposed to a local source. > Hot water boiler heating systems provide a clean and comfortable source of building heat that will also keep room air most in the drier winter months. The author does realize that these are typically sealed systems and don't boil water off into the air, right? I have several friends that use water heat, it's just as dry in their houses during the winter as it is in my forced-air heat residence.