Am I missing something here?

What you say is definitely true if the piping is insulated. Once its hot, its not absorbing any heat. So it can heat 426 sq ft of actively radiating surface.

However, if the pipes are continually radiating heat out, they will continue to absorb heat from the steam. In which case they need to be included in that 426 sq ft, and have impacts on the system beyond the heat needed to get the pipes up to temp. If I've got 400 sq ft edr of radiator, and 60 sq ft of radiating pipe, thats 460 sq feet of surface actively radiating. If each square foot of radiating surface gives off 240 BTU (assuming 70 degree room, 2psi steam at 215 degrees), then that requires a net heating capacity of 110K BTU. The EG-40 is rated at 426 * 240 = 103K BTU (which is the DOE rating),

Given that the pipes will continue to radiate 240 btu/sq ft once hot, I don't quite understand the idea that the pickup factor no longer applies when the pipes are hot, unless you mean that if the pipes and boiler are insulated, or have a sufficiently small effective radiating surface that radiative losses from them aren't significant.

I'm really trying to apply an engineering approach here. I'm more than welcome to be corrected, or shown a different way to calculate it. But 60 sq ft of piping uninsulated adds an additional 14.4K BTU of load. If its insulated it will add only a negligable amount at temperature. And it seems to me that should impact system design. Happy to learn otherwise if someone can explain it.

I am honestly sorry if my questions offended you. Truly. That was never my intention. I’m just trying to understand this. I’m just an engineer trying to talk to other engineers about an engineering problem. But I don’t think this has gone in a productive direction so I’ve learned my lesson. It’s just not my place to question these things. It’s seen as insulting. For that I’m truly sorry.