I have used both fires that were both round and rectangular and was curious what the real differences are. I have tried a few searches but I guess I'm using the wrong search terms since I haven't found anything discussing the shapes and the impact it has on the work being done. 

Mate I think the big difference is fuel economy. 

I'm not normally a solid fuel forge guy but I've never noticed a significant difference in the shapes. Some project might need a long narrow or big round fire but that argues for a duck's nest unless you have a lot to make.

Frosty The Lucky.

Where I started my apprenticeship they had long fires as they did a lot of springs, the job in hand dictates the shape of the fire that you build.  That is one of the advantages of a forge fire.

With a Coal fire, perhaps the shape and style of your Forge "Pot" ( Duck's Nest vs: Rivet type ) has the most impact on the efficiency of the fire.

Both of those are, of course, "Bottom Blast" Forges.

I don't have enough experience with "Side Blast" systems, to make intelligent comment on their characteristics, ... but would assume they would be more versatile, in regard to the shape of the fire.

 

Since I make it a "point", to never be in a hurry, ... I tend to keep my Forge Fire small and "manageable".

This is sometimes "counter-productive", ... but when you've eliminated any serious "Profit Motive" from your "Business Plan" ... it's not a problem.

 

.

 

 

The metal does not care how it gets hot, just that it does get hot before you start hitting on it.

The beauty of solid fuel is that you CAN adjust the shape of the fire for the project at hand. No one ever sid you could have only one forge. (grin)

Try explaining that your significant other, lol Glenn. 

A round pot doesn't fit brick work as easy as square, even tho an 8" round pot will hold less fuel (and fire doesnt naturally grow in square shapes) than a square pot. 

I appreciate your input guys. I had to ask because I'm building a new forge and I wanted to make sure there wasn't any big differences I needed to know about. I had planned on a rectangular fire pot since that's what I'm used to but didn't want to build it until I asked. 

If it's funnel shaped in cross section, the fire will follow the pot's shape to some degree.

The firepot is gonna be the kind with the trapezoid sides so the top is bigger than the bottom. I'm not sure just yet how big it's gonna be but I'm thinking about 8 inches long and 4 or so inches wide tapering down to maybe 7x3 inches.