The IRS has ruled that duct work is not a geo property eligible for the 30% tax credit. This according to Doug Dougherty president of the G.E.O.

I would assume the same is true for the radiation for hydronic systems, and storage buffers for desuperheater output too then?

The ruling was about duct work only to my knowledge. I believe the tax code language includes "plumbing".

From the EnergyStar website: What parts of a geothermal heat pump are covered by the tax credit? All geothermal heat pump components certified by the manufacturer in the "Manufacturer Certification Statement" will be covered by the 30% tax credit, as well as the installation costs associated with these components. There may be some add-on components that will not be covered such as an emergency back up system and the ducts. These components are not directly related to the efficiency of the covered geothermal heat pump property.

Hmmm ducts not related to the efficiency of a geothermal system.....right

I don't itemize my invoice to show the ductwork separate. I show one total for a ground source heat pump system Model Number XXX and Serial Number XXX and then has a total that includes all items necessary.