01What this calculator tells you
This calculator estimates the total electrical service load of a single-family home using the optional calculation in NFPA 70, the National Electrical Code (Article 220.82). Enter your living area, the number of small-appliance and laundry circuits, the nameplate volt-amps of your fixed appliances, and your heating and cooling loads.
You get the demand-adjusted general load, the governing heating-or-cooling load, the total in volt-amps, and — most usefully — the load converted to amps with a recommended standard service size and how much headroom it leaves. It mirrors the worksheets used by the U.S. Department of Energy and building departments nationwide.
02The 220.82(C) heating and cooling rule
The most common mistake in a home load calculation is adding the air-conditioning load and the electric-heat load together. The code does not allow that — because a house never runs full heat and full cooling at the same moment. Instead you take the single largest of the values below and ignore the rest.
03What counts as a fixed appliance
The “fixed appliances” field is the sum of the nameplate ratings of everything fastened in place. Volts × amps gives volt-amps; a wattage rating can be used directly as VA for this method. Typical values to add up:
Use each appliance’s actual nameplate where you can — these are typical figures, not a substitute for the label. Do not include the small-appliance, laundry, heating or cooling loads here; they have their own fields.
A load calculation is a sizing tool, not a full design. Treat the result as a starting point and confirm it with your local authority having jurisdiction.
- Optional method, single dwelling. This uses NEC 220.82. For an existing home you may use the 220.83 method; large or unusual homes may need the standard method (220.42/220.55).
- Nameplate accuracy. Your total is only as good as the appliance ratings you enter. A mis-entered range or water heater can shift the service size.
- Service minimum. The NEC sets a 100 A minimum for most dwellings (230.79), so the calculator never recommends below 100 A.
- Conductor and conduit sizing are separate. Once you know the service size, size the service conductors, grounding and raceway to match — check the raceway with our conduit fill calculator.
- Not a permit document. Building departments accept results on their own worksheets, stamped where required.
- Enter the heated living area in square feet (outside dimensions, excluding open porches and unfinished garages).
- Enter the number of small-appliance circuits (at least two) and laundry circuits.
- Add up the nameplate VA of every fixed appliance and enter the total.
- Enter your air-conditioning load and electric-heat load, and pick the heating type. Press Calculate.
The readout shows your demand-adjusted load, the governing HVAC load, the total, and the recommended service size with its headroom. Planning an addition or an EV charger? Increase the relevant load and recalculate to see whether your service still fits — then weigh the running costs with our energy efficiency upgrade calculator.
04Related calculators
Working through a related project? Try our Cable Tray Fill Calculator, Solar Panel Sizing Calculator, and Tankless Water Heater Sizing Calculator.
01The load calculation formula
The optional method builds one general load, discounts it with a single demand factor, then adds the larger of heating or cooling. All of it comes from NEC Article 220.82 — no per-circuit demand factors needed. The Department of Energy’s appliance-use figures help when a nameplate is missing.
Where:
- area= heated living area in square feet, outside dimensions.
- SA= number of 20 A small-appliance branch circuits (at least two).
- fixed appliances= summed nameplate VA of appliances fastened in place.
- factor= the 220.82(C) heating demand factor for your system (1.00, 0.65, or 0.40).
02Worked example
Take a 2,000 ft² home with 2 small-appliance circuits, 1 laundry circuit, 24,000 VA of fixed appliances, a 5,000 VA air conditioner and 10,000 VA of central electric heat. Work it one line at a time:
Swap in a heat pump (100% factor) or four-plus separately controlled heaters (40%) and Step 3 changes — but the cooling load would still only be used if it were the larger of the two. That single substitution is exactly why the 220.82(C) “largest of” rule matters.