The short answer
A 2,000 sq ft house with an electric range, dryer and water heater, a dishwasher and central air has a calculated load of 101 A by the NEC 220.82 optional method, so a 125 A service. Adding a 40 A EV charger takes it to 117 A (125 A); all-electric with a heat pump, backup heat and an EV charger, 156 A (200 A).
Service size by house size
Electric range (12,000 W), dryer, water heater and dishwasher, 5 kW of central air; then the same with a 40 A EV charger.
| House | Load | Service | With EV charger |
|---|---|---|---|
| 1,000 sq ft | 96 A | 100 A | 112 A → 125 A |
| 1,500 sq ft | 99 A | 100 A | 115 A → 125 A |
| 2,000 sq ft | 101 A | 125 A | 117 A → 125 A |
| 2,500 sq ft | 104 A | 125 A | 120 A → 125 A |
| 3,000 sq ft | 106 A | 125 A | 122 A → 125 A |
| 4,000 sq ft | 111 A | 125 A | 127 A → 150 A |
How it works
The formula
Not everything in a house runs at once, so the code counts the general load at a discount and adds only the biggest of the heating and cooling loads.
demand = first 10,000 VA + 40% of the rest + largest heating or cooling load
amps = demand ÷ 240 V
Assumptions
- NEC 220.82 optional method for a single-family dwelling, as laid out in EC&M's guide to dwelling load calculations: air conditioning at 100%; a heat pump at 100% plus 65% of its supplemental heat; electric heat at 65% for up to three separately controlled units, 40% for four or more. Only the largest counts.
- Appliance figures are examples: use each one's nameplate VA. A 40 A EV charger is 9,600 VA. A compressor's VA (volts × amps) is higher than its watts; include the indoor fan.
- Thermal storage heating counts at 100% under 220.82(C) and isn't covered here.
- Services: 100, 125, 150, 200, 225, 300, 400 A; NEC 230.79(C) sets 100 A as the minimum for a house.
- Code editions and local amendments differ; your electrician's calculation is the one that counts.
Worked example: 2,000 sq ft, electric appliances, central air
- 2,000 × 3 = 6,000 VA + 3 × 1,500 = 4,500 + appliances 22,700 W = 33,200 VA
- 10,000 + 40% × 23,200 = 19,280 VA + 5,000 VA air = 24,280 VA
- 24,280 ÷ 240 = 101 A → 125 A service
Too big or too small
- Too small: tripped mains and no room to grow. An EV charger, heat pump or induction range can push a full panel over.
- Before upgrading, check load management. Devices that pause an EV charger or water heater when the house is busy are allowed by the NEC and can save a service upgrade.
- The panel and the utility both matter. The service wires, meter and panel all need the rating; the utility may need to upgrade its transformer.
Questions people ask
Do I need a 100 or 200 amp service?
Work out the load. A 2,000 sq ft house with an electric range, dryer and water heater and central air comes to 101 A by the NEC optional method, so a 125 A service. Add a 40 A EV charger and it's 117 A, a 125 A service.
Can I add an EV charger to a 100 amp panel?
Sometimes. Run the numbers with the charger included: if the total stays under the service rating, it fits. If not, a load management device that pauses the charger when the house is busy, or a lower charging current, may avoid an upgrade.
Does a heat pump need a bigger service?
The NEC counts the heat pump at 100% plus 65% of its backup heat strips, instead of the air conditioner. In the example house a heat pump with 10 kW of backup brings the load to 126 A (150 A service).
What is the NEC optional method?
Section 220.82 lets a single-family house's service be sized by a simpler calculation: 3 VA per sq ft for lights and outlets, 1,500 VA for each kitchen and laundry circuit, the nameplate of every fixed appliance, the first 10 kVA of that at 100% and the rest at 40%, plus the largest heating or cooling load.
Why is the minimum 100 amps?
NEC 230.79(C) requires at least a 100 A service for a one-family house, whatever the calculated load.