220.83 optional calcs - exist dwelling unit

[malachi constant]

2008 NEC. For 220.83(B), where additional electricla space heating is to be installed...

I assume you count existing units and new units? That seems self-evident.

I have an application where there are two existing elec space heating units, and up to three new units being added. If there were less than four it is obvious how to calculate: "less than four separately controlled space-heating units"...shall be figured at 100%.

But what if there are four or more? Code does not say. I assume either:
(A) only the first three are counted at 100%, everything after that is ignored... OR...
(B) just count them all at 100%.

To be safe I'm going with (B) 100%. Still come up less than 100A on an existing 100A panel, but it's close and if a couple nameplates turn out to be a little higher than expected we'll need an upgrade. Any thoughts?

 

[charlie b]

I think that after you count 100% of the first three, the fourth and any others fall under the next two classifications (100% of the next 8 kVA, and 40% of anything beyond that). In other words, you lump the fourth and fifth separately controlled heating systems with the small appliance circuits, the ranges, the water heaters, and the rest.