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NEC 220.83 calculator and calculation explained

Updated 2026-11-03 · Step-by-step explanation of the NEC 220.83 existing dwelling load calculation (120.83 in NEC 2026), the (A) vs (B) split, and how it compares with 220.82 and 220.87.

220.83 is the code's shortcut for existing homes. It is permissive: you can always do a full new-construction calculation instead, and sometimes that comes out lower.

Step by step (2020/2023)

  1. General lighting: 3 VA per square foot of living area.
  2. Small-appliance and laundry circuits: 1,500 VA each (at least two kitchen circuits plus one laundry).
  3. Nameplates: every appliance fastened in place or on its own circuit: range, oven, cooktop, dryer, water heater, dishwasher, disposal, A/C, heat, chargers, spas.
  4. Pick the subsection. If you are not adding heating or A/C, use (A): first 8 kVA at 100%, the rest at 40%. If you are adding heating or A/C, use (B): the larger of heating or cooling at 100%, all other loads 8 kVA at 100% and the remainder at 40%.
  5. Divide by 240 V and compare with the service rating.

The 2026 version (120.83)

One table instead of two. Existing loads: first 8 kVA at 100%, remainder at 40%. New EVSE and new central resistance heat: 80%. Other new loads, including heat pumps and A/C: 50%. Lighting is 2 VA per sq ft. Only the larger of heating or cooling counts (Intrysys: NEC 2026 changes from NEC 2023; Electrical License Renewal: 120.83 Existing Dwelling Units (2026 summary)).

Our calculator fills the first 8 kVA with existing loads first and then new loads with the lowest factor first, which is the conservative reading of the 2026 table. Your AHJ may read it differently.

Comparing methods

MethodBest when
220.83 / 120.83 existing dwellingAdding a load to an existing house
220.82 / 120.82 optionalWhole-house recalculation; first tier 10 kVA in 2023, so it can come out lower
220.87 / 120.87 measuredYou have 12 months of utility peak demand data

Run these numbers in the calculator →

Common questions

What is the 220.83 demand factor?

In the 2020 and 2023 editions, the first 8 kVA of load counts at 100% and the remainder at 40%. When adding heating or A/C, the larger of heating or cooling counts at 100%.

What changed in 2026?

The section became 120.83, lighting dropped to 2 VA per sq ft, and new loads got their own factors: EVSE and central resistance heat at 80%, other new loads at 50%.

Estimate only; a licensed electrician and your local authority having jurisdiction decide; not an engineering stamp.

Taking it to your electrician or the permit desk? The worksheet is free to print. A formatted permit-style PDF with a saved house is $9 one-time; electricians get branded PDFs, unlimited jobs and client links with Pro at $19/month.

Sources

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