rmh heat channels - 26 gauge vs 30 gauge

I've gotten some salvaged stove pipe to use in an rmh.  The instructions I'm following specify 26 gauge and I'd like to follow a proven design as closely as possible.

I *think* it's 26 gauge but can't be 100% sure. This is just 2 5-foot lengths; the other pieces I have I know definitely are 26 gauge.

What would be the ramifications if those 2 pieces are actually 30 gauge?  
Can I afford to take a chance on it? I haven't seen a discussion of this anywhere but if there is one, a pointer to it would be appreciated.

Thanks, all!  

The first 5' or so after the manifold in a standard RMH are recommended to be 26 gauge, as is the first piece of stovepipe that rises up out of the mass to go to the chimney, but the rest can be pretty much anything as long as it can support the cob while it is wet.

Hi Susana ; The only places you will need of heavy gauge pipe are, one piece entering your mass (this is because of the heat there) and you want another piece popping up out of your mass ( just to protect it from damage) All other pipe buried in your mass or going vertical indoors can be (thin wall) HVAC pipe.

Thank you both!  That's exactly the information I need.