Dwelling Service Load Calculator
NEC 220.82 optional method. Calculates total demand load in VA and amps, then suggests a standard service size. Free, no account required.
Dwelling Details
Outside dimensions, excludes open porches and unfinished garage.
Minimum 2 per NEC 210.11(C)(1). 1,500 VA each.
Minimum 1 per NEC 210.11(C)(2). 1,500 VA each.
Sum of nameplate VA for fastened-in-place appliances, ranges, ovens, dryers, water heater, dishwasher, disposal, etc.
Only the larger of heat or A/C is used (NEC 220.82(C)).
84.2 A demand
Recommended minimum service size: 100 A
NEC 220.82 Optional Method Reference
- 220.82(A): Applies to a dwelling unit served by a single 120/240V or 208Y/120V set of 3-wire service or feeder conductors with an ampacity of 100 or greater.
- 220.82(B): Demand factor: 100% of the first 10 kVA, 40% of the remainder.
- 220.82(C): Use the larger of heating or air conditioning, never both.
- 220.12: 3 VA per sq ft for general lighting (dwelling).
- 220.52: 1,500 VA per small appliance circuit and per laundry circuit.
When to use the standard method instead
Use NEC 220 Part III (standard method) if the dwelling has fewer than 100 A service, multiple dwelling units sharing a feeder, or if your AHJ requires it. The optional method (220.82) typically yields a smaller service size because of the 40% demand factor on everything past 10 kVA.
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This calculator uses NEC 2023 Article 220 Part III optional method for dwellings. Always verify with your local AHJ and the NEC edition adopted in your jurisdiction. Not a substitute for a stamped load calculation on a permitted project.
How the dwelling service load (optional method) calculation works
220.82 is the optional calculation for a one-family dwelling served by a single 120/240 V or 208Y/120 V set of service conductors rated 100 A or greater. It exists because the standard method in Part III of Article 220 is long, and for an ordinary house the optional method lands in the same place with far less work.
The method has two parts that get added at the end. The general load is 3 VA per square foot of floor area, plus 1,500 VA for each 2-wire small-appliance and laundry branch circuit required by 210.11(C), plus the nameplate rating of every fastened-in-place appliance, plus motors and low-power-factor loads. That total gets the 220.82(B) demand factors: 100 percent of the first 10 kVA and 40 percent of everything above it.
The heating and air conditioning load in 220.82(C) is calculated separately and never demand-factored the same way. You take the largest of the listed options, which include 100 percent of the nameplate of air conditioning and cooling, 100 percent of the heat pump compressor with supplemental heat, 65 percent of central electric space heating, and 40 percent of separately controlled electric space heating with four or more units. Add that to the demand-factored general load and divide by 240 to get service amps.
Step by step
- 1
General lighting and receptacles
3 VA per square foot of habitable area, excluding open porches, garages, and unused spaces, per 220.82(B)(1).
- 2
Small appliance and laundry
1,500 VA per circuit. Minimum two small-appliance circuits and one laundry circuit under 210.11(C).
- 3
Fastened appliances
Nameplate VA of range, oven, dryer, water heater, dishwasher, disposal, and similar, per 220.82(B)(3).
- 4
Apply the demand factor
First 10,000 VA at 100 percent, remainder at 40 percent, per 220.82(B).
- 5
Heating or cooling, largest only
220.82(C). Take the single largest of the six listed options. Heat and A/C are not added together.
- 6
Convert and size
Total VA divided by 240 V gives amps. Round up to a standard service size, minimum 100 A for a one-family dwelling per 230.79(C).
Worked example
A 2,000 square foot dwelling with two small-appliance circuits, one laundry circuit, a 12 kW range, a 4.5 kW water heater, a 5 kW dryer, a 1.2 kW dishwasher, and 9 kW of central electric heat. Size the service by the optional method.
- General lighting: 2,000 x 3 = 6,000 VA.
- Small appliance and laundry: 3 x 1,500 = 4,500 VA.
- Appliances: 12,000 + 4,500 + 5,000 + 1,200 = 22,700 VA.
- General total = 6,000 + 4,500 + 22,700 = 33,200 VA.
- Demand: first 10,000 at 100 percent = 10,000. Remainder 23,200 x 0.40 = 9,280. Subtotal 19,280 VA.
- Heat, 220.82(C): 9,000 x 0.65 = 5,850 VA.
- Total = 19,280 + 5,850 = 25,130 VA. 25,130 / 240 = 104.7 A.
Answer: 104.7 A calculated, so a 125 A service is the next standard size that serves it. A 100 A service would not.
How this is tested on the exam
Load calculation is the highest-point-value topic on most master exams and shows up on journeyman exams as well. The two decisions that determine whether you get it right are choosing the correct method, optional under 220.82 versus standard under Part III, and remembering that heating and cooling under 220.82(C) is largest-of, never a sum. Read the question for the phrase optional method or standard method before touching a number.
Frequently asked questions
When can I use the optional method instead of the standard method?
220.82 applies to a one-family dwelling, or an individual unit of a multifamily dwelling, served by a single 120/240 V or 208Y/120 V set of service or feeder conductors with an ampacity of 100 A or greater. Outside those conditions you use the standard method in Part III of Article 220.
Do I add electric heat and air conditioning together?
No. 220.82(C) says to use the largest of the listed selections. Because a house does not heat and cool at the same time, you take whichever single load is greater and ignore the other.
Is the range taken at nameplate or from Table 220.55?
Under the optional method of 220.82 you use the full nameplate rating of the range in the general load before applying the 10 kVA and 40 percent demand factors. Table 220.55 demand factors belong to the standard method in 220.55, not to 220.82.
What is the minimum service size for a house?
230.79(C) requires the service disconnecting means for a one-family dwelling to be rated not less than 100 A, three-wire. Your calculation may of course require more.