Definition
The NEC Article 220 math that determines whether your electrical service can carry your home's appliances — the gate for EV chargers, heat pumps, and panel upgrades.
What does a load calculation actually add up?
Square footage (general lighting load), the required small-appliance and laundry circuits, every fixed appliance's nameplate rating, and the largest heating or cooling load — run through the NEC's demand factors, which recognize that not everything runs at once. The result in amps is compared against your service size (60, 100, 125, or 200 amps). It's arithmetic, not opinion — two electricians running it honestly get the same answer.
Why does it matter before an EV charger or heat pump?
Because those are the two biggest loads a home adds in decades — a Level 2 charger alone draws 40–60 amps. On many older 100-amp services the calculation comes back over the limit, and the honest options become a service upgrade, a smaller charger, or a load-management device that sheds the charger while the dryer runs. Skipping the math and hoping is how mains breakers end up tripping on winter evenings.
Can you estimate it yourself?
You can get usefully close. Our free online load calculator walks the same Article 220 structure with plain-language inputs and tells you whether you're comfortably inside your service, near the line, or over it. The permitted version — signed by a licensed electrician — is what the city and the utility accept when an upgrade or new circuit is actually filed.
In the Puget Sound
Western Washington's electrification push makes this the region's most-run calculation: heat pumps replacing gas furnaces and EV chargers landing in 1960s–70s Eastside homes that still carry 100-amp services.
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Trade: Electrical