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 and primarily designed to reduce the heat gain of such dwelling unit. (4) Manufactured homes included The term dwelling unit includes a manufactured home which conforms to Federal Manufactured Home Construction and Safety Standards (part 3280 of title 24, Code of Federal Regulations). (d) Residential energy property expenditures For purposes of this section— (1) In general The term residential energy property expenditures means expenditures made by the taxpayer for qualified energy property which is— (A) installed on or in connection with 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), and (B) originally placed in service by the taxpayer. Such term includes expenditures for labor costs properly allocable to the onsite preparation, assembly, or original installation of the property. (2) Qualified energy property (A) In general The term qualified energy property means— (i) energy-efficient building property, (ii) a qualified natural gas, propane, or oil furnace or hot water boiler, or (iii) an advanced main air circulating fan. (B) Performance and quality standards Property described under subparagraph (A) shall meet the performance and quality standards, and the certification requirements (if any), which— (i) have been prescribed by the Secretary by regulations (after consultation with the Secretary of Energy or the Administrator of the Environmental Protection Agency, as appropriate), and (ii) are in effect at the time of the acquisition of the property, or at the time of the completion of the construction, reconstruction, or erection of the property, as the case may be. (C) Requirements and standards for air conditioners and heat pumps The standards and