its 4 inches in dia
no I did not design it ( I am not good enough with the stress calculation and material knowledge to do so ) I can build them OK but the design i leave to others
It was built from a GLR design I just order the copper kit from them ,beat up the tube plates flanges got it good and hot and stuck it together
BTW the info on their site it at total variance to the drawings you get they state its a 45 psi unit the plans call it a a 90 pound SWP unit , then the go on to tell you to test to 200 psi hydro the last bit is wrong the max first test should be 180psi.
to sort it out I did correspond with the designer and ran the plans past out clubs boiler inspector who did the calcs and said test to 160 SWP at 80 and retest at 120 psi
the drawings do contain an unmakeable component the fire hole tube is not able to be made as drawn , and the safety valve is a dead weight one not a spring one
Please note with boilers ALWAYS consult with your clubs boiler inspector at the start , during and testing the boiler ,these are not things to mess with without the help of a boiler inspector
BTW that unit is gas fired using a Polly ceramic burner
Stuart