You mean 50 CFM (a rate of flow, cubic feet of air per minute) at 0” or no back pressure. I can virtually guarantee that this wont provide 30 CFM at the burner.
Do you know what flow you need to get the heat output you want? For a medium sized forge, one not large enough to warrant a ribbon burner, I think about 30 CFM is a minimum to get it hot in a reasonable time.
There is a ton of math required here. You figure out your forge volume, and from that estimate your BTU output requirement (you could do the thermo for this, but others have done it for you and it is hard).
Next, determine air flow required by figuring out your volumetric gas flow (at one atmosphere) for that heat, based on that, multiply the gas flow by 5 (o2 per propane molicule) and again by 5 (for the concentration of O2 in air).
If you are at altitude, you will need to compensate for lower density.
Based on that flow rate you need to work backwards to figure out your static pressure in the system. This is ridiculously hard math for something like a ribbon burner, but use solidworks or some other volumetric flow modeling software and you can get a good answer somewhat easily. Based on that static pressure, find a blower that can provide the flow you need.
So the math is a pain. And because there are some imprecise numbers involved (original BTU requirement, burner inefficiency, static pressure estimation - variations in internal surfaces in your plumbing can have a meaningful effect) you are gonna want to probably double this number.
I have done this math for normal burners and it is a bit of a pain. It would be harder by far for a ribbon burner. I am not sure what your time is worth, but I am guessing it is more than you will save over a $100 blower that you are confident will work.
And finally, because the blower lists only one data point (flow with no back pressure) it is impossible to mathematically interpolate what that flow would be at some other level of back pressure. I might be able to giess if I saw the blower design. If you do want to interpolate, you need a minimum of 2 points, preferably at least 3 and ideally 5. As far as i remember, for any blower design, there is not a direct relationship between static pressure and flow. It is probably negative exponental regression.
