Step-through NEC 220 residential load calculation · Code section at every step
2200 sq ft × 3 VA = 6,600 VA
2 circuits × 1,500 VA = 3,000 VA (min. 2 circuits)
1 circuit(s) × 1,500 VA = 1,500 VA (min. 1 circuit)
First 3,000 VA at 100%, next up to 120,000 VA at 35%. Combined: 11,100 VA → 5835 VA
Nameplate: 12.0 kW → demand: 8.0 kW (NEC 220.55 Col C, single unit)
Nameplate: 5.5 kW, 100% demand (single unit, min 5 kVA)
Heating or cooling (whichever is larger): 3.6 kW at 100%
Water heater: 4.5 kW + other: 1.5 kW. 75% demand if ≥4 appliances.
Total demand: 28.9 kVA ÷ 240V = 121 A → select 150A service
This simulator steps through the NEC Article 220 residential load calculation procedure, showing the applicable code section at each step and the cumulative demand load. Engineers and electricians use it to correctly size service entrance equipment and ensure compliance with the National Electrical Code for residential dwelling units.
NEC Article 220 requires a systematic demand-based calculation rather than simply summing all connected loads. The method applies demand factors that reflect that not all loads operate simultaneously at full capacity. The calculation proceeds in sequence: (1) General lighting at 3 VA/sq ft (NEC 220.12); (2) Small appliance circuits at 1,500 VA each, minimum 2 circuits (NEC 220.52(A)); (3) Laundry circuit at 1,500 VA, minimum 1 circuit (NEC 220.52(B)); (4) Apply demand factor to the combined Steps 1–3 per NEC Table 220.42 — first 3,000 VA at 100%, remainder at 35% up to 120,000 VA.
Fixed appliances are then added at their nameplate ratings: electric range with NEC 220.55 demand factors (8 kW for a single range rated ≥8.75 kW), electric dryer at 100% (min 5 kVA, NEC 220.54), HVAC using only the largest heating or cooling load (NEC 220.60), and fixed appliances at 75% if four or more are present (NEC 220.53). The total demand load is then divided by the service voltage (240V single-phase) to find the minimum service amperes, rounded up to a standard size per NEC 230.79.
NEC Article 220 governs branch circuit, feeder, and service load calculations. NEC 220.82 provides an optional simplified method for existing dwelling unit services. NEC 230.79 defines minimum service sizes (100A minimum for single-family dwellings per most jurisdictions). NEC 310.15 governs conductor ampacity. ANSI C84.1 sets voltage tolerances. Local amendments may increase minimum service sizes — many jurisdictions now require 200A minimum service for new construction to accommodate EV charging and heat pump loads.
The NEC standard method tends to produce conservative results — the optional method (NEC 220.82) often yields a smaller calculated load for existing dwellings. When sizing for EV charging (EVSE), the load must be added at 100% of the EVSE branch circuit rating per NEC 220.12 unless a demand management system is in place. Heat pumps with supplemental electric heat must include the supplemental heat at 100% unless interlocked.
For new construction with anticipated electrification (EV, heat pump water heater, induction range, battery storage), engineers should consider sizing the service for 400A split into two 200A panels to avoid future service upgrades. NEC 220.82 cannot be used if any single appliance exceeds 50% of the existing service ampacity.
Enter the dwelling unit floor area, number of small appliance and laundry circuits, and nameplate ratings for all major appliances. Click "All Steps" to see the complete calculation at once, or "Step-Through" to advance one NEC code section at a time and review the rationale for each demand factor. The running demand total updates at each step. Use the final service size recommendation as the minimum — local jurisdiction requirements may mandate a larger service.
NEC Table 220.12 specifies 3 VA/sq ft as the unit load for dwelling units, based on historical data for typical residential lighting density. This accounts for portable lighting and general-use receptacles. The value has not changed in decades, but modern LED lighting actually draws far less — the 3 VA/sq ft is a conservative planning figure.
NEC Table 220.42 applies a demand factor to the combined lighting, small appliance, and laundry load: the first 3,000 VA is at 100%, the next 117,000 VA (up to 120,000 VA total) is at 35%, and anything above 120,000 VA is at 25%. This reflects the statistical improbability of all lighting circuits operating simultaneously at full load.
NEC 220.82 (optional method) may be used for new or existing single-family dwellings. It uses a simpler two-tier approach: first 10 kVA of general loads at 100%, remainder at 40%, plus air conditioning or heating at 100% (whichever is larger). It typically yields a smaller calculated load than the standard method and is widely accepted for service sizing.
EVSE (Electric Vehicle Supply Equipment) branch circuits must be included in the load calculation. A 240V/48A Level 2 EVSE circuit contributes 48 × 240 = 11,520 VA (11.5 kW) at 100% demand. If a demand management system (load control) is provided, the NEC allows a reduced demand based on the controlled load. This is one of the most significant factors driving service upgrades from 100A to 200A in existing homes.
NEC 230.79(C) requires a minimum 100A, 3-wire service for single-family dwellings. However, most jurisdictions and the 2023 NEC cycle trends toward 200A minimums for new construction to accommodate modern electrical loads. The calculated load from Article 220 may indicate a larger service is needed — the service must be rated at or above the calculated demand.
Try our Electrical Studio
More calculators, simulators, and guides for this discipline.