Water-to-water heat pumps, supplied from geothermal earth loops, represent a growing sector of the hydronic heat source market. Most current-generation models can produce water temperatures up to about 125° F, perhaps a little higher if you’re willing to push the compressor operating envelope. That temperature is very “workable” for a variety of heat emitters, including several types of radiant floor, wall and ceiling panels, and properly sized panel radiators or fan coils.
Water-to-water heat pumps can also produce chilled water in a typical temperature range of 45-55° F for cooling. That opens up many opportunities for a single installer to provide a “total hydronic solution” for space heating, domestic water heating and cooling.