When can I use the 220.82 optional method?

NEC 220.82 may be used when the dwelling is supplied by a single set of 120/240 V or 208Y/120 V three-wire service conductors with an ampacity of 100 A or greater. It is a faster alternative to the standard 220.42 method and usually yields a slightly smaller service.

How is the general load demand factor applied?

Under 220.82(B) the sum of general lighting (3 VA per square foot), the two small-appliance and one laundry circuits (4500 VA), and all appliance nameplates is taken at 100 percent for the first 10 kVA and 40 percent for everything above 10 kVA. This single factor replaces the multi-tier standard tables.

Why are heating and cooling not added together?

NEC 220.82(C) recognizes that a home never runs heating and air conditioning at the same time, so you include only the larger of the two. The tool compares the cooling load against the heating component and carries forward whichever is greater.

What heating demand factor should I choose?

Central electric space heating is taken at 65 percent. A heat pump with supplemental heat, or four or more separately controlled electric heating units, is taken at 100 percent. Picking the right type matters because it can change the service size by a full step.

How do I convert the result to a service size?

Divide the total demand VA by 240 volts to get amperes, then round up to the next standard service: 100, 125, 150, or 200 A. The optional method commonly lets a typical all-electric home fit on a 200 A service.

Residential Optional Load Calculation (NEC 220.82)

The NEC 220.82 optional method is the quick way to size a dwelling service for a permit. Instead of the multi-tier standard tables, it sums everything, applies one simple demand factor, and adds only the larger of heating or cooling. This calculator runs that method end to end.

How it works

The general load is built from three pieces and then demand-factored:

general      = 3 VA/sq ft × floor area
small-appl   = 4500 VA  (two 1500 VA SA circuits + one 1500 VA laundry)
appliances   = total nameplate VA of fastened appliances, range, dryer, WH
gross        = general + small-appl + appliances

demand load  = first 10 kVA of gross @ 100% + remainder @ 40%

Then the HVAC component per 220.82(C) is the larger of the cooling load or the heating load (65 percent for central electric heat, 100 percent for a heat pump with supplemental heat or four-plus separately controlled units). The total is the demand general load plus that HVAC component, and the service amps are the total divided by 240 V.

Worked example

A 2,000 sq ft all-electric home with 18 kVA of appliances, 5 kVA of cooling, and 10 kVA of central electric heat: general gross is roughly 28,500 VA, which demand-factors to about 17,400 VA. Heating at 65 percent (6,500 VA) beats cooling (5,000 VA), so 6,500 VA is added, giving about 23,900 VA, or near 100 A — which rounds up to a 100 or 125 A service depending on margin.

Notes

Use this method only where the service qualifies — a single 120/240 V or 208Y/120 V three-wire service of 100 A or more. Never add heating and cooling together, and always round the computed amperes up to the next standard service rating before selecting equipment and conductors.