We spent ~$3K having the insulation in our 30-year old home replaced. However, TurboTax says we can't get the Home Energy Credit. Original owners of one home.

First, make sure you have completed the rest of your return. The energy credit is non-refundable, so if you don't have enough income tax being computed, the credit will be limited. Also double-check all the questions about the location of the house in the US and the living in the house are answered. 

Next, let's revisit the entry, and make sure the expenses are listed in the correct place, because some other energy-efficient improvements have lower credits available. You would have needed to spend at least $4,000 on the insulation to receive the maximum credit of $1,200.  The available credit is 30% of the cost, not to exceed $1,200. So for your cost of about $3,000, the credit should be about $900.

1. Upon opening TurboTax, choose Deductions & Credits

2. Locate Your Home 

3. Start/Revisit Home Energy Credits

4. On the Energy Efficient Home Improvements screen, select Yes then Continue. 

5. Answer the next few questions until you get to Did you have any of these qualified energy efficiency improvements in 2024?  Insulation material or air sealing system is listed here.  Select Yes and continue.

6. Make sure you enter the total cost and answer the questions about ownership and location of the home.