Fannie/Freddie, FHA, VA standards-partly ducted forced-air heat?

[Harriet Baldwin]

Question: does anyone know if there are Fannie/Freddie, FHA or VA rules that require a forced air system to be ducted to all parts of the house? Or is there a standard that allows non-ducted registers for 2nd floor areas?

Older homes in our area often have a functioning forced air furnace with ducts for all 1st floor rooms but gravity registers (basically holes-with-grills through the 1st fl ceiling/2nd fl floor) for the 2nd floor.  I assume these systems were mostly updates of old octopus systems (fully gravity fed).

Local HVAC guys suggest leaving as-is unless someone wants to put AC in - but if we can avoid limiting the (future) borrowers to non-conforming products, that would be good!