220.83 · is the existing service big enough?
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Worked example — for an existing 1,800 ft² dwelling on a 100 A service, 6,000 VA of appliances, 240 V, the engine returns:
46 A by 220.83(A) — 11,160 VA · existing 100 A service is adequate
How it works. Adding load to an existing dwelling does not mean recalculating the house from scratch. 220.83 works from the existing connected load plus whatever is being added, and the demand factor depends on whether air conditioning or electric space heating is part of that addition. The practical question it answers is whether the service already in place is still big enough.
What this covers: 220.83 applies to a 120/240 V or 208Y/120 V 3-wire service only. Under (B) there is no code row for four or more separately controlled space-heating units — that combination fails rather than guessing, because the plausible readings differ by 60 points.
Educational reference, not code. Based on NEC (NFPA 70) 2023 (220.83). Your state or local AHJ may enforce a different edition or amend it — theirs is the one that counts. No NEC text is reproduced here.