Round top inner firebox

Flattop or round top fireboxes, what are the advantage of each type?

I look forward to some replys

Ian,

I am no expert but here are a few that I know of;

A flat top inner firebox will allow more tubes to be fitted. Apparently, the first third of the tubes length from the firebox is the most effective for transferring the heat, so the more tubes, the better the heat exchange.

The larger outer surface area of the square inner firebox will again allow more heat transfer to take place.

The disadvantage is that the flatter, squarer inner and outer firebox surfaces will need more support in the from of stays. So it could be seen as being slightly more difficult to build. Conversely, the curved surfaces of the round firebox are slightly easier to form and build.

Also, the outer firebox of the simple round topped boiler can obviously be formed using a straightforward length of tube - just cut and open out the sides.

The front firebox to barrel plate on a flat topped boiler is more difficult to form and build.

I am sure more experts will come and add or maybe even dispute what I have written but I think I have captured at least some of the pros and conns.

Phil H

Ian you have a PM see Inbox on green line at top of this page

Roy

Im mid build on a couple of 5" gauge Sweetpea boilers which have totally round fire boxes. No stays of any kind for the firebox tube is a massive bonus - both end plates are stayed. If the top of a conventional type loco boiler is half round no stays are needed in it (joing sides and ends stayed as usual) but as stated previously you lose a lot of tube space compared to a square section plate.

To Phil H, Many thank for your thoughts on inner fire boxes, it answers many of my thoughts.

Ian