Dwelling service load calculation

Pick the edition and the method, or start from a preset: the houses of NEC Informative Annex D’s examples D1(a), D1(b), D2(a), D2(b) and D2(c), a gas-heated house, an all-electric house with a heat pump and an EV charger, an older house on 100 A getting an EV charger, and a 150 A house swapping its furnace for a heat pump.

Then describe the house: floor area (outside dimensions, not porches, garages or unfinished space), small-appliance and laundry circuits, cooking appliances (kW), electric dryers, fixed appliances (water heater, dishwasher, disposer, built-in microwave, blowers, pumps, hot tub — tick motor for motors), heating and cooling (A/C, heat pump with its strip heat, baseboard with the number of separately controlled units, thermal storage) and EV chargers (their current setting).

The cards at the top show the calculated load, the current, the service size and the neutral. The worksheet below lists every step the way the Annex D examples do — section, calculation, VA — with the service conductors at 83 % (310.12(A)). Print prints the worksheet alone; CSV downloads it.

The methods:

Why at the bottom explains each rule with its section. The 2026 edition renumbers Article 220 as Article 120; the tool cites the numbering of the edition you pick.

The tests reproduce D1(a) (18 600 VA, 77.5 A, a 100 A service, neutral 60.6 A), D2(a) (21 480 VA, 89.5 A), D2(b) (six room air conditioners — 29 200 VA taking them at 240 V, 28 780 VA in editions that took them at 230 V, a 125 A service either way) and D2(c) (heat pump with 15 kW of supplemental heat, 34 790 VA, 150 A). Annex D’s D1(b) is the D1(a) house with two room air conditioners, a disposer and a dishwasher, worked in amperes line by line with each 120 V load on a chosen line; the tool works in VA with 120 V loads spread evenly (24 000 VA, 100 A), so its preset for that house comes out lower than the book’s per-line figures — the book’s way is the more conservative one for an unevenly loaded panel. The 2026 numbers are checked against a published 2026 study example (6000 ft², 39 878 VA, 175 A).

The panel schedule lays the circuits into a panel and balances it — Start a panel schedule sends it these loads as circuits, and Size a backup generator sends the appliances, heating, cooling and chargers to generator sizing; motor branch circuit sizes a pump or compressor circuit; wire size and voltage drop picks the service conductors for a long run; grounding and bonding covers the grounding electrode conductor; heat loss sizes the heat pump; shop power plans a workshop subpanel’s circuits.

Any current browser, on a phone or a desktop; it works offline once loaded. Print prints the worksheet alone.

Everything runs in your browser and the house is kept in its local storage. Nothing is sent anywhere; Share link puts the house in the link itself.