energy conservation measure
(4) The term “energy conservation measure” means a measure which modifies any building, building system, energy consuming device associated with the building, or industrial plant, the construction of which has been completed prior to May 1, 1989 , if such measure has been determined by means of an energy audit or by the Secretary, by rule under section 6325(e)(1) of this title , to be likely to maintain or improve the efficiency of energy use and to reduce energy costs (as calculated on the basis of energy costs reasonably projected over time, as determined by the Secretary) in an amount sufficient to enable a person to recover the total cost of purchasing and installing such measure (without regard to any tax benefit or Federal financial assistance applicable thereto) within the period of— (A) the useful life of the modification involved, as determined by the Secretary, or (B) 15 years after the purchase and installation of such measure, whichever is less. Such term does not include (i) the purchase or installation of any appliance, (ii) any conversion from one fuel or source of energy to another which is of a type which the Secretary, by rule, determines is ineligible on the basis that such type of conversion is inconsistent with national policy with respect to energy conservation or reduction of imports of fuels, or (iii) any measure, or type of measure, which the Secretary determines does not have as its primary purpose an improvement in efficiency of energy use.