Too many variables to answer with a broad brush stroke. Just the method of earth coupling can dramatically change the ratings. For example, a ClimateMaster 5-ton, 2-stage split unit has the following ratings:
1st/2nd stage
Cooling EER Heating COP
Open water source or standing column well: 25.7/19.2 4.4/4.3
Closed loop water system: 15.8/14.5 5.2/4.7
Ground loop: 22.2/15.3 4.0/3.6
http://www.ahridirectory.org/ahridir...ultSearch.aspx
You can see all the ratings for this unit at the ARI website if you put in the manufacturer as Climatemaster and the equipment model no. as TTS064 <Search>. As you can see, the efficiencies can vary substantially. As for cost, we've found that in comparison to a multi-stage hybrid heat system (gas furnace w/air-to-air HP) the equipment costs are about the same. The ducted system costs are the same to the main variable is the earth coupling. In our case that a standing column well with pump/control/wiring costs. Those costs always vary wildly with the size of the system.
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