Limitation on residential energy property expenditures The amount of the credit allowed under this section by reason of subsection (a)(2) shall not exceed— (A) $50 for any advanced main air circulating fan, (B) $150 for any qualified natural gas, propane, or oil furnace or hot water boiler, and (C) $300 for any item of energy-efficient building property. (c) Qualified energy efficiency improvements For purposes of this section— (1) In general The term qualified energy efficiency improvements means any energy efficient building envelope component, if— (A) such component is installed in or on a dwelling unit located in the United States and owned and used by the taxpayer as the taxpayer's principal residence (within the meaning of section 121), (B) the original use of such component commences with the taxpayer, and (C) such component reasonably can be expected to remain in use for at least 5 years. (2) Energy efficient building envelope component The term energy efficient building envelope component means a building envelope component which meets— (A) applicable Energy Star program requirements, in the case of a roof or roof products, (B) version 6.0 Energy Star program requirements, in the case of an exterior window, a skylight, or an exterior door, and (C) the prescriptive criteria for such component established by the 2009 International Energy Conservation Code, as such Code (including supplements) is in effect on the date of the enactment of the American Recovery and Reinvestment Tax Act of 2009, in the case of any other component. (3) Building envelope component The term building envelope component means— (A) any insulation material or system which is specifically and primarily designed to reduce the heat loss or gain of a dwelling unit when installed in or on such dwelling unit, (B) exterior windows (including skylights), (C) exterior doors, and (D) any metal roof or asphalt roof installed on a dwelling unit, but only if such roof has appropriate pigmented coatings or cooling granules which are specifically