Evan wrote:

Clearly you are not informed about all the types and flavors of HVAC
equipment out there... 2" duct work is quite common in retrofit
applications and uses a higher pressure fan system to move the air...
The 2" duct hose can be fished through walls without breaking into
them in most situations... The smaller sized duct hoses are used
with the systems that have the small round outlets in the ceiling
where you would need one outlet per set amount of square footage
in each room depending on your building's heat loss/gain conditions...

I would guess that the higher velocity air from a 2" duct would be
quite noisy. How is the noise controlled?