2005 home,2500sqft, USA, texas. HVAC, problems.

5ton AC split, Nordyne, in top shape.

I failed at measuring my bad duct (supply) ROUND. attic all.

The HWH hot water heater failed hard, and the replacement guy crushed my approx size 10" HVAC vent supply,

the problem is the Duct size here, is wrong.

the duct pipe measures, 29" circumference. (metal to metal , 2" insulation on outside removed)

divided by Pi, 3.14 is 9.23 inches, diameter, D= pi/C

I am at a total loss here. 8,10,12, normal sizes do not match.

10" new duct measures 32" circum. as expected.

thanks for any clues , hints are directions to solving this riddle.

I.M

PS: if I google 9" duct , zero hits for sold metal pipe.