The tax credit for energy efficiency is available for improvements made to a home that you own and use as your "principal residence." This is the home where you live most of the time. A temporary absence due to special circumstances, such as illness, education, business, military service, or vacation will not change your principal residence.

The home must be in the United States. It can include a house, houseboat, mobile home, cooperative apartment, condominium, and a manufactured home.

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The law (Section 25C(c)(1)(A)) specifies: 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