Per taxpayer.
See this IRS website for more information - https://www.irs.gov/credits-deductions/individuals/nonbusiness-energy-property-credit
Nonbusiness Energy Property Credit (Section 25C) at a Glance
A credit of 10 percent of the cost of qualified energy-efficient improvements. Qualified improvements include adding insulation, energy-efficient exterior windows and doors, and certain roofs. The cost of installing these items is not included in the credit calculation. Additionally, a credit is available, including the costs of installation, for certain high-efficiency heating and air-conditioning systems, as well as high-efficiency water heaters and stoves that burn biomass fuel. There is a lifetime limitation of $500, of which only $200 may be used for windows. Qualifying improvements must have been placed in service in the taxpayer's principal residence located in the United States through Dec. 31, 2016.
See IRS Form 5695 Instructions - https://www.irs.gov/instructions/i5695/ch01.html#d0e153
Joint occupancy.
If you owned your home jointly with someone other than your spouse, each owner must complete his or her own Form 5695. To figure the credit, there are no maximum qualifying costs for insulation, exterior doors, and a metal or asphalt roof. Enter the amounts you paid for these items on the appropriate lines of Form 5695, Part II. For windows and residential energy property costs, the amount allocable to you is the smaller of:
The amount you paid, or
The maximum qualifying cost* of the property multiplied by a fraction. The numerator is the amount you paid and the denominator is the total amount paid by you and all other owners.
*$2,000 for windows; $300 for energy-efficient building property; $150 for qualified natural gas, propane, or oil furnace or hot water boiler; or $50 for an advanced main air circulating fan.
