I moved this to a new thread since, while still relevant for the homeowner who wanted some advise, is getting off topic. AHRI/ISO 13256 rating is done at 32F EWT for heating geothermal heat pumps. http://www.waterfurnace.com/literature/5series/SC2500AN.pdf for dual stage (water furnace). Page 6 gives you the rating, page 8 tells you what is included in the rated COP, including 68F entering air temp. http://www.waterfurnace.com/literature/5series/SC2506WN.pdf for w-w, page 27 gives you the 13256 -2 rating standard table with 32F EWT and 104 entering load temp. For a 4 ton unit as I mentioned as an example, COP is 3.1 for the water-water unit versus 4.0 of the water-air unit. 22.5% less efficient for the w-w. Just by example: Hydronic water air handler (water furnace) http://www.waterfurnace.com/literature/envision/SC1008HN.pdf Page 17 gives you the capacity at different water temps. Using again the 4 ton example, the air handler needs 120F water to put out 39,000 BTUs. They are usually rated at 114F entering water temp. So the numbers are very real. The rating standard used to compare units across the board uses 32F EWT as a standard. I challenge you to find an air handler which puts out its nominal rating below 114F . Fan power is partially included in the 13256-1 rating, the fan power of the air handler is not, dragging your COP down further. You don't seem to understand that a system which has to go through an additional heat exchange step (refrigerant to water to air) will be inherently less efficient than a simpler refrigerant to air process, especially when the higher operational temperatures are needed for the water-water units to have any air handler perform at the rated capacity.