Originally Posted by SlickTX
Natgas is delivered in a low pressure state so I don't think the line diameter will effect anything except the volume of gas provided.
Because NatGas is delivered at low pressure, the volume
of gas has everything
to do with how much heat your burners can crank out.
Disclaimer: always seek the help of a professional plumber when working with NG. That being said, I am not a plumber, but I have been using NG for brewing for the past 5 years, and I can tell you from my experience, size matters. That is to say, use 3/4 inch pipe leading out to your rig, and then adapt the pipe down as close to the burners as you can.
For my setup, I am using two NG fired BG14 burners. I plumbed 3/4 inch black pipe out to the brew rig, then use 1/2 inch black pipe for the last 12-inches leading up to the gas valves, and then 3/8 inch flex line to the burner orifice. I have had no problems controlling the burners using gas ball valves as opposed to the smaller needle valves.
Here you can see the short 1/2-inch pipe (which is plumbed to the larger 3/4-inch pipe just out of the bottom of the photo), 1/2-inch ball valve with 1/2 x 3/8 flare adaptor and 3/8 flex line. Bigger pipe and valve deliver better performance at wide open, and the ball valves provide adequate control at lower settings. 3/4-inch black pipe is not much more expensive than the 1/2 inch, and well worth the cost.