The Tranquility 27 Series geothermal heat pump is ClimateMaster’s latest and most efficient unit, with an EER rating of 27. The unit uses a zero-ozone-depletion refrigerant, has a two-stage blower motor, and comes standard with a MERV 11 filter system. A 4-ton unit costs $5,180, independent of the required ground loop. ClimateMaster, 877/436-6263,

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