For the time being, the 25C residential energy tax credit is extinct. 25C, also known as the Existing Home Retrofit Tax Credit, officially expired Dec. 31, 2011, leaving homeowners without a tax benefit rewarding residential energy efficiency improvements for the first time since 2008. Since many HVAC residential contractors used the tax credit as a selling tool, there has been a lot of discussion about how the expiration will affect the industry, and if there is any hope for an extension of the credit.