Residential Load Calculator (NEC 220.82)
Enter the floor area, the fixed appliances and the heating and air-conditioning loads of a house, and get the calculated load in volt-amperes and amps at 240 V and the standard service size that covers it, using the NEC 220.82 optional method for a single-family dwelling. The breakdown table shows every line of the calculation.
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Read the how-to guide
The optional method (NEC 220.82)
- General loads: 3 VA per square foot for lighting and receptacles, plus 1,500 VA for each small-appliance and laundry circuit, plus the nameplate rating of every appliance that is fastened in place, permanently connected or on its own circuit (range, oven, dryer, water heater, dishwasher, disposal and so on).
- Demand factor: the first 10,000 VA of that total at 100%, and everything above it at 40%.
- Heating or cooling: add the larger of 100% of the air-conditioning load or 65% of the central electric space heating (220.82(C)). Heat pumps with supplemental heat, thermal storage and four or more separately controlled heating units have their own percentages in 220.82(C).
- Amps = total VA ÷ 240 V. The service is the next standard rating at or above that (100, 125, 150, 200, 225, 300 or 400 A), with 100 A the minimum for a one-family dwelling under 230.79(C).
The optional method may be used for a single-family dwelling with a 120/240 V (or 208Y/120 V) 3-wire service or feeder of 100 A or more. The standard method in 220.40 through 220.61 gives a different, usually higher, figure, and some jurisdictions or utilities require it. Service conductors are then sized from the load (310.12 allows 83% of the service rating for a dwelling).
Worked example
A 2,000 sq ft house with two small-appliance circuits, one laundry circuit, a 12 kW range, 5 kW dryer, 4.5 kW water heater, 1.2 kW dishwasher, 800 VA disposal, 1.5 kW microwave, a 5 kVA air conditioner and gas heat: general loads 6,000 + 3,000 + 1,500 + 25,000 = 35,500 VA. First 10,000 at 100% plus 25,500 at 40% = 20,200 VA. Add the 5,000 VA air conditioner: 25,200 VA, or 105.0 A, so a 125 A service covers it. With a 10 kW electric furnace instead of gas, 65% of 10,000 = 6,500 VA replaces the 5,000 VA of AC: 26,700 VA, 111.3 A, still 125 A.
Frequently asked questions
Why is a 200 A service so common if the calculation says 125 A?
The optional method is generous with demand factors, and 200 A panels cost little more than 125 A. Most new houses get 200 A for future loads such as EV chargers, heat pumps and hot tubs, and some utilities require it.
Which square footage do I use?
The floor area measured from the outside dimensions of the house, counting every floor that is finished or could be finished, but not open porches, garages or unused, unfinished spaces.
Do I enter 8 kW for the range like the standard method?
No. The optional method uses the nameplate rating of the range and the other appliances; the 40% demand factor above 10 kVA does the reducing. The 8 kW figure comes from Table 220.55 in the standard method.
How do I handle a heat pump?
Under 220.82(C) a heat pump without supplemental heat counts at 100% like an air conditioner. With supplemental strip heat, use 100% of the compressor plus 65% of the strips unless the controls prevent both from running at once. Enter the combined figure in the heating field in that case.
Does this size the feeder to a subpanel or an existing service?
The same method applies to a feeder serving the whole dwelling. For an existing dwelling with added loads, 220.83 has a similar optional method. An engineer or the inspector may require the standard method for anything unusual.
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This calculator gives an estimate for planning and is not tax, legal or engineering advice. Confirm code-related results against the code edition adopted in your jurisdiction and with your authority having jurisdiction, and follow the manufacturer's instructions.