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Electrical Load Calculation: NEC Article 220
Why This Matters
Service upgrades, new homes, and big new loads like EV chargers usually need a load calculation, and many inspectors ask to see it. NEC Article 220 gives two ways to do it for a dwelling: the standard method (Part III) and the optional method (220.82). They don’t give the same number. The optional method is shorter and usually comes out lower, and you can use whichever one your jurisdiction accepts.
This is different from wire sizing and voltage drop. Those size individual circuits. This sizes the whole service. If you need to convert nameplate watts to amps, the watts-to-amps calculator handles that.
The section numbers below are from the 2020 NEC, the edition the 2021 IRC’s electrical chapters are based on. Check which edition your area has adopted.
Standard Method (NEC 220.40 through 220.61)
Add up every load, apply the demand factors, and divide by voltage.
Step 1: General Lighting and Receptacles
NEC Table 220.12 assigns 3 VA per square foot of living space. For a 2,400 sq ft house:
2,400 x 3 = 7,200 VA
Step 2: Small Appliance and Laundry Circuits
NEC 220.52 adds 1,500 VA for each 20-amp small appliance circuit (at least two) and 1,500 VA for the laundry circuit.
2 kitchen circuits x 1,500 VA = 3,000 VA 1 laundry circuit x 1,500 VA = 1,500 VA
Total: 4,500 VA
Step 3: Apply the Demand Factor to Steps 1 and 2
7,200 + 4,500 = 11,700 VA.
NEC Table 220.42:
- First 3,000 VA at 100% = 3,000 VA
- Remaining 8,700 VA at 35% = 3,045 VA
Total after demand: 6,045 VA
Step 4: Fixed Appliances
Use nameplate ratings. A typical list:
- Dishwasher: 1,500 VA
- Garbage disposal: 960 VA (8 amps x 120V)
- Bathroom exhaust fans (total): 240 VA
- Garage door opener: 600 VA
- Hardwired microwave: 1,500 VA
NEC 220.53: with four or more fastened-in-place appliances (not counting ranges, dryers, and space heating or cooling), you can take 75% of their total.
4,800 VA x 0.75 = 3,600 VA
Step 5: Range
NEC Table 220.55, Column C: one range rated 12 kW or less counts as 8 kW (8,000 VA).
Over 12 kW, Note 1 raises the Column C value by 5% for each kW, or major fraction of a kW, above 12. A 14.4 kW range is 2.4 kW over. The 0.4 isn’t a major fraction, so that’s 2 kW, or 10%:
8,000 x 1.10 = 8,800 VA
Step 6: Dryer
NEC 220.54: 5,000 VA or the nameplate rating, whichever is larger.
Step 7: Heating and Cooling
NEC 220.60: heating and cooling don’t run together, so count only the larger of the two. Electric heat counts at 100% in the standard method (220.51).
A heat pump with electric backup strips is the catch. The compressor and strips can run at the same time, so they count together. A 6,000 VA compressor with 10 kW strips is 16,000 VA. That’s larger than the 5,000 VA cooling load, so 16,000 VA goes in.
Many calculations also add 25% of the largest motor, because 220.50 sends motor loads to 430.24. Here that’s the 6,000 VA compressor, so 1,500 VA. Ask your inspector whether they expect it.
Step 8: Water Heater
A standard 50-gallon electric water heater is about 4,500 VA. Electric tankless units run 18,000 to 36,000 VA, which is why they often force a service upgrade.
Step 9: Total
| Load | VA |
|---|---|
| General lighting + small appliance (after demand) | 6,045 |
| Fixed appliances (75%) | 3,600 |
| Range (14.4 kW) | 8,800 |
| Dryer | 5,000 |
| Heat pump + strips | 16,000 |
| 25% of largest motor | 1,500 |
| Water heater | 4,500 |
| Total | 45,445 VA |
45,445 / 240 V = 189 amps. That’s a 200-amp service.
Optional Method (NEC 220.82)
Step 1: General Loads
Add, at nameplate: 3 VA per sq ft, 1,500 VA per small appliance and laundry circuit, and every fastened-in-place appliance, range, dryer, and water heater. Leave out heating and cooling; they come in Step 3.
For the same house: 7,200 + 4,500 + 4,800 + 14,400 + 5,000 + 4,500 = 40,400 VA.
Step 2: Demand Factor
NEC 220.82(B): first 10,000 VA at 100%, the rest at 40%.
10,000 + (30,400 x 0.40) = 10,000 + 12,160 = 22,160 VA
Step 3: Heating and Cooling
NEC 220.82(C) takes the largest of six options. For a heat pump with supplemental strips, option (3) is 100% of the compressor plus 65% of the electric heat:
6,000 + (10,000 x 0.65) = 12,500 VA
That beats the 5,000 VA cooling load, so it’s the one you use.
Total
22,160 + 12,500 = 34,660 VA
34,660 / 240 = 144 amps. The optional method lands well below the standard method’s 189 amps. A 150-amp service would pass under this method, where the standard method needs 200.
EV Chargers
A Level 2 charger is a continuous load, counted at its full nameplate: 7,680 VA for a 32-amp unit, 11,520 VA for 48 amps. Added to the standard-method total above, that’s 53,125 to 56,965 VA, or 221 to 237 amps. That house would need more than 200 amps unless something changes.
Two things can change it. The optional method’s 40% demand factor applies to the EV load too, and an automatic load management system can cap what the charger draws. NEC 625.42 (2020) lets the service calculation use the limit set by that system, and the 2023 NEC added broader energy management rules in 220.70. Your local inspector decides which edition and which approach applies.
The Quick Way
Trussly’s Service Load calculator runs the optional method from NEC 220.82 (IRC E3602.2). Enter the square footage, small appliance and laundry circuits, appliance nameplate ratings, and your heating and cooling equipment, and it shows the calculated load and the minimum service size. Use it to check your numbers, then confirm with your inspector before you order a panel.