Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Drawings look fine Frank!

There is also a design where the flue makes a 180 degree turn inside the boiler and comes back out at the end where it started, either through the end cap or out the top of the boiler, just like your drawings show only at the left end.

I suspect you may capture a bit more heat in your boiler water with the flue making its 90 degree turn inside the boiler, and at the same time allow for a bit of "super heating" with the part of the flue going vertical through the upper part of the boiler where there is no water but only steam. I doubt either of those "effects" amount to much on our little model boilers however!

I also suspect that it is much easier to simply run the flue through both end caps instead of finagling an elbow and curved surface joint necessitated by exiting out the top of the boiler.