I have been through all that-- I know I can use my current system. I just
need to know about the under slab ductwork.

wrote in message
oups.com...
Your better off installing a seperate furnace and AC unit. You might be
better off to use tubing in the slab for heat.

have you checked to see your existing furnace and AC has the capacity
for your addition? Espically with the catherdral cieling.