"Christian Fox" wrote in message
...
In article ,
says...
We can't *see* it from here, your best bet is to call your local,
*competent*, licensed, insured, professionally trained, HVAC technician to
assess your needs and properly install a correctly sized furnace for your
maximum comfort and minimum utility bills.

Read my original post. I'm not getting a new furnace right away. I'm
finishing my
basement right away. I don't want to cover up the ducts, only to find out
that they need
to get changed after the basement ceiling has been drywalled.

So, I'll simplify the question: Can a high-efficiency natural gas furnace
use the same
ductwork as a 15-year old, standard-efficiency furnace?

I'll simplify the answer... I can't *see* it from here.... and I don't know
if the system was sized and installed correctly in the first place.
Now, as far as finishing the basement *before* you have the HVAC work done,
you are putting the cart before the horse. There is a reason why the HVAC
techs and installers work their magic *BEFORE* the sheetrock goes up.