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Residential electrical load calculator
Estimate total amperage demand using NEC standard load calculation method to size a residential service panel (100A vs 200A).
Service amps required
@ 240 V
Show the work
- Total VA demand35,540
- General lighting + circuits VA11,100
- Appliances VA (after demand factor)8,740
- HVAC + EV VA (100% per NEC)15,700
NEC service-panel sizing — the optional method
Building inspectors size residential services using NEC 220.82 (the optional method) because the standard method overestimates real-world load. The optional method applies a demand factor — not every appliance runs full-tilt simultaneously — and treats HVAC + EV at 100%.
What the calc does
- General lighting + small-appliance circuits: 3 VA × heated sqft, plus 1,500 VA per small-appliance and laundry circuit (minimum 3 circuits per code).
- Appliances: nameplate kW for range, water heater, dryer, fixed loads.
- Demand factor: first 10,000 VA at 100%, everything above at 40% (optional method).
- HVAC + EV: full nameplate, no discount. EV charging especially counts at 100% because it can run alongside HVAC.
Total VA / 240 V = required service amperage. Round up to the next standard panel size: 100, 125, 150, 200, 320/400.
When 200A isn't enough anymore
Heat pumps + EV chargers are why new builds are spec'd at 200A or even 320/400A. A 1990s house with gas heat, gas range, and gas dryer fits in 100A easily. Add a heat pump (8 kW) and a 48A EV charger (11.5 kW) and you're suddenly looking at 60+ amps of "always at 100%" load on top of the rest of the house.
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