The federal $500 Nonbusiness Energy Property Tax Credit is currently expired, and we don't know when (or if) Congress will approve this credit for tax year 2018. This credit covered energy-efficient improvements like windows, doors, skylights, insulation, roofing products, nonsolar water heaters, heating, ventilating, and cooling systems. If this credit is approved after your file your 2018 return, you can file an amendment to claim the credit. Another option is to postpone filing your return until Congress definitively approves or denies this credit for tax year 2018.