That's good.

 

I posted for you in another thread a response to the same question. International Mechanical Code.

603.4 Metallic ducts

Depending on the geometrical shape and size will dictate the minimum gauge size. 28 gauge being the lightest not 30

 

30 ga. for 6" round branch runs is acceptable and industry standard.

 

International Mechanical Code
Table 603.4

Round ducts and enclosed rectangular ducts 14 inches or less minimum thickness 0.0157 equivalent galvanized gauge size 28.

M1601.1.1 Above-ground duct systems.
Above-ground duct systems shall conform to the following:
4. Minimum thickness of metal duct material shall be as listed in Table M1601.1.1(2). Galvanized steel shall conform to ASTM A 653. Metallic ducts shall be fabricated in accordance with SMACNA Duct Construction Standards Metal and Flexible.

International Residential Code
TABLE M1601.1.1(2) GAGES OF METAL DUCTS AND PLENUMS USED FOR HEATING OR COOLING
Same verbiage.


SMACNA table 2-1

28 gauge

Would you consider SMACNA HVAC Duct Construction Standard to be the industry standard and the two codes that are sited to be industry standards?

 

make sure they seal it all. it sounds like you already don't trust them. why?

 

Then EVERY residential HVAC installation in eastern Ohio and western Pennsylvania is in direct violation of IMC. Every one. I have been building, designing and installing residential sheet metal duct systems for over 40 years and not ONCE in those 40 some years has one local OR State inspector called me or any other mechanical contractor I know (and it's dozens) on using 30 gauge galvanized piping for branch runs. My lay outs and plans are submitted to the county building inspection department for review BEFORE any permits are issued. They inspect everything starting at rough in and they pay attention, I've been turned down for being 1/8" to close to a combustible with a 30' run of type B metal vent, they don't miss details.

 

I think this is a recent change. In the last couple of years all the distributors here have stopped stocking 30ga duct.

IMO, there was never ever anything wrong with 30ga.

 

I like to use 26 for everything but round pipe is usually 30ga and works fine, larger sizes 26 and all square/rectangle 26.