firebox to cook chamber opening

[opieb123]

Hey everyone I have a question on opening from firebox to tank was running numbers on calc. And sq inches for opening is 185.19 which if I went 27" across and 7" up from bottom would give just over for what I need and I should have 7" at other end of baffle plate my question could the opening to firebox be bigger with out changing the size at end of baffle

[Gizmo]

Theoretically no. In practice I have run smaller BP gaps before but on an adjustable design where I could change it. If you are going with a fixed gap then stay with the same opening or as close as practical to the size of your throat.

[opieb123]

Thanks, the only reason im asking is I have been looking at some of the fuel oil tank builds and it seems like there firebox to cook chamber are bigger then they should