Service Load Calculation (NEC 220.82 Optional Method)
Optional-method dwelling demand (first 10 kVA at 100% + remainder at 40% + larger HVAC).
Example
You enter
- Dwelling area (ft²) 2400
- Small-appliance circuits 2
- Laundry circuits 1
- Fixed appliances (kW total) 3
- Range / cooktop (kW) 12
- Dryer (kW) 5.5
- Water heater (kW) 4.5
- Heating (kW) 9
- Cooling (kW) 5
- Service voltage 240
You get
- General demand (VA) 20680
- Optional-method total (VA) 29680
- Optional-method demand (A) 123.7
Checked against published worked examples from: NFPA; IAEI Magazine (International Association of Electrical Inspectors).
Details, formula, and sources
ScopeCompared to the standard Part III method (Table 220.45).
Formula or tableGeneral load demand = first 10 kVA at 100% + remainder at 40%, where general load = 3 VA/ft^2 + 1500 VA per small-appliance and laundry circuit + nameplate of fixed appliances, range, dryer, water heater. HVAC is the larger of cooling at 100% and heating at 100% (heat pump), 65% (central resistance or fewer than 4 separately controlled units) or 40% (4 or more separately controlled units) (220.82(C)).
Source and editionNEC 2023 (NFPA 70). 220.82 (optional dwelling load calculation); the Part III standard method (Table 220.45 lighting demand) for the comparison.
Free accessFree read-only access at nfpa.org/freeaccess.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesarea_ft2, small_appliance_circuits, laundry_circuits, fixed_appliances_kw, range_kw, dryer_kw, water_heater_kw, hvac_heating_kw, hvac_cooling_kw, service_voltage, general_demand_va, optional_total_va, optional_demand_a
- Method choice the optional method may be used for a dwelling served by a single 120/240 V or 120/208 V set of service conductors; size to the larger of the optional and standard methodsNEC 2023 220.82 / Table 220.45
- HVAC the larger of cooling at 100% and heating at 100% (heat-pump compressor), 65% (central resistance, or fewer than 4 separately controlled units) or 40% (4 or more separately controlled units); non-simultaneous loads are not summedNEC 2023 220.82(C)