@Eric-td wrote:
actually I have found that the key to getting the tax credit is to replace the entire geothermal operating system, meaning condenser unit + air handler.
There is no such limitation in the actual law. See section 25D, paragraph (d)(5) for the definition of qualifying heat pump property.
https://www.law.cornell.edu/uscode/text/26/25D
I agree a repair does not qualify, but there is nothing in the law that says that replacement of part of a system doesn't count.
There could be a regulation or FAQ that says you can only get credit for an entire system, but when the regulations or instructions conflict with the Law, the law is always primary.
If you found something on the IRS web site that it must be an entire system, I would like the link to see for myself. If you found advice on a non-IRS web site, I would not consider it to be authoritative. Many energy savings sites get the law wrong.
