All geothermal heat pump components certified by the manufacturer in the "Manufacturer Certification Statement" will be covered by the 30% tax credit, as well as the installation costs associated with these components. There may be some add-on components that will not be covered such as an emergency back up system and the ducts. These components are not directly related to the efficiency of the covered geothermal heat pump property.
IRS Guidance: Notice 2009-41 Section 3. (1)(e) Qualified geothermal heat pump property expenditures are expenditures for equipment which uses the ground or ground water as a thermal energy source to heat the dwelling unit or as a thermal energy sink to cool the dwelling unit, meets the requirements of the Energy Star program which are in effect at the time that the expenditure for such equipment is actually made (even if under § 25D(e)(8) the expenditure is deemed made at a later time for purposes of determining the taxable year for which a taxpayer may claim the credit), and is installed on or in connection with a qualifying dwelling unit.