So, I am trying to insert a "Wtr-to-Air HP Elec Backup" into my model, either a plant loop or an air loop, but neither will accept it when dragging it over. Both pop up the error "The selected component is not allowed at this location."

I have looked at the WSHP measures, and at least one of them seems to work, though it makes little sense to me. So I was just wanting to see if I can create such a system from scratch. Any clues would be appreciated.