I am in the process of getting quotes for solar, replacing windows, and replacing AC. I have had two companies give quotes for combining these installs, one doing solar and windows, and the other doing all three. In both cases they state that the 26% tax credit would be applied to the total amount financed (solar, windows, and AC or any combination thereof). Therefor, the tax credit would be applied to the windows and AC install, lowering the cost of those pieces as well as the solar system if everything was done as one project and financed under the same loan.
Is this a thing, or are they straight up lying to get more business?
They are either mistaken, or are lying.
Only the Solar gets the 26% credit.
However, you MIGHT qualify for a different tax credit for the windows and A/C (assuming they have the proper energy savings criteria). However, that is subject to a LIFETIME maximum of $500. I think the credit started around 2006-ish, so you may have already 'used up' that credit, which includes other energy savings things like insulation and a furnace. If you have already used up the full $500, then you would not qualify for anything for the windows and A/C (at least not on the Federal return, but there could be other credits through your State or your utility company).
This link to the TurboTax page Energy Tax Credit: Which Home Improvements Qualify? has information regarding available energy tax credits that you may find useful.
**Mark the post that answers your question by clicking on "Mark as Best Answer"