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Electric Load Calculator

NEC demand-factor electrical load analysis. Calculate total electrical load in watts and amperes using NEC Article 220 demand factors for general lighting, HVAC, small appliances, and large loads.

Building Inputs

ft²
VA/W
VA/W

Fixed Appliances

VA
VA
VA
VA

Service Voltage

General Lighting

6,000 VA

Raw NEC Load

10,500 VA

Demand-Adjusted

5,625 VA

Fixed Appliances

23,200 VA

HVAC Load (larger)

14,000 VA

Total Demand VA

42,825 VA

Minimum Service

178.4 A

Recommended Panel

200 A

NEC 230.79 minimum service sizing

NEC 220.42 demand factors applied: 100% on first 3,000 VA · 35% on next 117,000 VA · 25% on remainder. HVAC uses larger of heating vs cooling per NEC 220.60.

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Solution Methodology

01

Enter Floor Area

Input gross square footage — general lighting load = 3 VA/ft² for residential.

02

Add Branch Circuits

Include small-appliance (2 × 1,500 VA) and laundry (1,500 VA) branch circuit loads.

03

Apply NEC Demand Factors

Use NEC Table 220.42: 100% on first 3,000 VA, 35% on next 117,000 VA, 25% on remainder.

04

Add Fixed & HVAC Loads

Sum 100% nameplate ratings for fixed appliances and include larger of heating or cooling.

05

Compute Service Ampacity

Divide total demand VA by service voltage (240 V single-phase) to determine minimum amps.

Common Questions

What is a demand factor in electrical calculations?
A demand factor is the ratio of the maximum demand on a system to the total connected load. Because not all loads run simultaneously at full capacity, the NEC allows you to reduce the connected load by a demand factor percentage when sizing conductors and service equipment. For example, the NEC applies a 35% demand factor to general lighting loads between 3,001 VA and 120,000 VA for dwelling units.
How do I calculate the electrical load for a house?
Per NEC 220.12, start with 3 VA × gross square footage for general lighting. Add two 1,500-VA small-appliance circuits and one 1,500-VA laundry circuit. Apply NEC Table 220.42 demand factors (100% on first 3,000 VA, 35% on next 117,000 VA). Add 100% of the nameplate rating for all fixed appliances and the larger of heating or cooling load. Divide the total VA by the service voltage to get amps.
What service panel size do I need?
Most modern single-family homes require 200-amp service. If the calculated total demand load divided by 240 V is less than 100 A, a 100-amp panel may suffice; 101–160 A suggests 150–200 A service. EV chargers, hot tubs, and electric vehicles may push requirements to 320–400 A for high-demand homes.
Should I use heating or cooling load for HVAC in the NEC calculation?
NEC 220.60 (non-coincident loads) allows you to omit the smaller of two loads that will never run simultaneously. For most climates, you include 100% of the larger HVAC load (whichever of heating or cooling draws more amperes) and exclude the smaller one from the service calculation.