First... "hydronic" means forced hot water and a boiler (not a furnace)
Second... hydronic and boilers have NOTHING to do with AC
To start... Go take a photo of what you have and post it here.
Include the make and a model # too.
Not true. There are air handlers with hot water coils and evaporator coils....... Unlikely though that it is in an unconditioned space (attic)