An electrical load calculation is the arithmetic that shows a building department the service you are installing is big enough for what the building will use. For a new South Florida house it is usually part of the permit submittal, alongside a riser diagram and panel schedule, and it decides whether you order a 150-amp, 200-amp or larger service. A search for "load calculation" often turns up HVAC sizing (Manual J), which is a different calculation; this guide is about the electrical one under Article 220 of the National Electrical Code (Mike Holt on Article 220).
Florida enforces the 2020 NEC today through the Florida Building Code 8th Edition (FBC-Residential 2023, E3401.1). Below: the two methods for a dwelling, a worked example for an illustrative South Florida house, what changes for existing homes, and a note on the 2023 NEC. It is part of our South Florida electrical permits, codes and inspections guide.
Two methods: standard and optional
Article 220 gives a dwelling two ways to calculate the service or feeder load: the standard method in Part III and the optional method in Part IV, per Mike Holt on 2020 NEC dwelling calculations.
Standard method (Part III)
The standard method starts with the same building blocks as the optional one: 3 VA per square foot for general lighting and general-use receptacles, two 1,500 VA small-appliance circuits and one 1,500 VA laundry circuit (Mike Holt, 2020 NEC). It then applies a separate rule to each load type (Mike Holt, Load Calculations Part 2):
- Table 220.42 demand factors on the general lighting load (Mike Holt).
- 220.53: a 75 percent demand factor on four or more fastened-in-place appliances rated 1/4 hp or 500 watts or more, not counting cooking equipment, dryers, space heating or air conditioning (Mike Holt).
- 220.54: dryers at 5,000 watts (VA) or the nameplate rating if higher (Mike Holt).
- 220.55: household cooking appliances over 1.75 kW use the Table 220.55 demand factors and notes (Mike Holt).
- 220.60: where two loads are unlikely to run together, such as heating and cooling, only the larger counts (Mike Holt).
The standard method is more work. EC&M's dwelling calculation article describes it as "almost impossible without software" for a full house (EC&M, dwelling load calculations).
Optional method (220.82)
The optional method in 220.82 is simpler and is what many new-house calculations use. It works in three steps (Mike Holt, 2020 NEC optional method):
- Add the general loads: 3 VA per square foot, 1,500 VA for each of the two small-appliance circuits and the laundry circuit, every fixed appliance at nameplate, and motors at 100 percent of nameplate VA (Mike Holt, 2020 NEC optional method).
- Take the first 10 kVA of that total at 100 percent and the remainder at 40 percent (Mike Holt, 2020 NEC optional method).
- Add the largest of the heating and air-conditioning loads: 100 percent of the air-conditioning nameplate, a heat pump with 65 percent of supplemental heat, or space heating at 65 percent for fewer than four separately controlled units and 40 percent for four or more (Mike Holt, 2020 NEC optional method).
The optional method is only for a dwelling served by a single 120/240-volt or 120/208-volt, 3-wire set of service or feeder conductors with an ampacity of 100 amperes or more (Mike Holt, 2020 NEC optional method).
Worked example: an illustrative South Florida house
All numbers below are illustrative, chosen to show the arithmetic. They are not a design for any real house; your electrical contractor uses the actual square footage and equipment nameplates. The method follows 220.82 as summarized by Mike Holt for the 2020 NEC.
The house: 2,400 square feet, central air conditioning with a 5 kW heat strip in the air handler, a pool pump, an electric water heater, an electric range and dryer, a dishwasher and a 48-amp EV charger, on a 120/240-volt service.
Step 1: general loads
| Load (illustrative) | Basis | VA |
|---|---|---|
| General lighting and receptacles | 2,400 sq ft x 3 VA | 7,200 |
| Small-appliance circuits | 2 x 1,500 VA | 3,000 |
| Laundry circuit | 1 x 1,500 VA | 1,500 |
| Range (nameplate) | 12 kW | 12,000 |
| Dryer (nameplate) | 5 kW | 5,000 |
| Electric water heater (nameplate) | 4.5 kW | 4,500 |
| Dishwasher (nameplate) | 1.2 kW | 1,200 |
| Pool pump motor (nameplate VA) | 2,000 VA | 2,000 |
| EV charger (nameplate) | 48 A x 240 V | 11,520 |
| Total general load | 47,920 |
Step 2: apply the demand factors
- First 10,000 VA at 100 percent: 10,000 VA.
- Remainder: 47,920 - 10,000 = 37,920 VA; 37,920 x 0.40 = 15,168 VA.
- General load after demand: 10,000 + 15,168 = 25,168 VA.
Step 3: add the larger of cooling or heating
- Air conditioning (illustrative nameplate for the condenser and air handler): 7,000 VA at 100 percent = 7,000 VA.
- Heat strip: 5,000 VA x 0.65 = 3,250 VA.
- The larger is the air conditioning: 7,000 VA.
Step 4: total and amperes
- Total calculated load: 25,168 + 7,000 = 32,168 VA.
- At 240 volts: 32,168 / 240 = about 134 amperes.
On these illustrative numbers, the calculated load is about 134 amperes, so the service and its conductors must be rated for at least that. Many builders choose a larger service for future loads such as a second EV charger or a generator; that is a planning choice, and your electrical contractor and the plan reviewer confirm the final size. Note how much the EV charger moves the number: without it, the general load would be 36,400 VA and the result about 115 amperes (36,400 - 10,000 = 26,400 x 0.40 = 10,560; 10,000 + 10,560 + 7,000 = 27,560 VA / 240).
Existing homes: 220.83 and 220.87
For additions and new equipment in an existing house, two other routes exist. 220.83 is an optional calculation for existing dwellings, and 220.87 lets you use one year of maximum-demand data at 125 percent, plus the new load, to check whether the existing service can take it (EC&M, optional feeder and service calculations). These are common when adding an EV charger, a pool or an ADU; see panel upgrades and EV charger permits in South Florida.
A 2023 NEC note: EV chargers
The 2023 NEC adds 220.57, which sets the EVSE load at the larger of 7,200 watts or the nameplate, and 220.70, which lets an energy management system setpoint be used in the calculation (Leviton Captain Code 2023). The 2023 NEC is not yet in force in Florida: it arrives with the 9th Edition, proposed to take effect December 31, 2026 (Florida Administrative Register). In the example above the 11,520 VA charger already exceeds 7,200 watts, so the 7,200-watt floor would not raise it. See our 9th Edition electrical changes guide.
What reviewers want to see
- The method named (standard or optional) and the code edition.
- Square footage matching the architectural plans.
- Every fixed appliance and motor listed with its nameplate rating.
- A result that matches the service size on the riser diagram and panel schedule.
Requirements differ by department, so use the checklist of the department with jurisdiction: Miami-Dade County (unincorporated areas; each city has its own building official), Broward County ePermits and the Palm Beach County Building Division. More in our electrical plan review guide and 2020 NEC new home checklist.
Questions builders ask
Is a load calculation required for a residential electrical permit?
Submittal requirements vary, so check your building department's checklist. Broward's generator policy, for example, lists an NEC 220 load calculation with the riser diagram (BORA Policy 06-03 as used by Lauderdale-by-the-Sea).
Which method gives a smaller service?
It depends on the house, so run both if the service size is close to a breakpoint. The optional 220.82 method takes only 40 percent of the general load above the first 10 kVA (Mike Holt, 2020 NEC), which is why it is popular for appliance-heavy homes. Your contractor picks the method that fits the job.
Does the pool pump count?
Yes. In the optional method, motors are included at 100 percent of nameplate VA in the general load (Mike Holt, 2020 NEC).
Can I use the calculation from my HVAC contractor?
No. A Manual J sizes the cooling equipment. The electrical load calculation uses the equipment nameplate that results from it.
See also electrical planning and dedicated circuits.
Need a load calculation for a permit? Send us the plans and equipment list, or call (305) 359-7312. KRW Electric Company LLC (Florida certified electrical contractor EC13012832) handles the permit and the inspection on its jobs across Miami-Dade, Broward and Palm Beach counties.
Reviewed by Kyle White, KRW Electric Company LLC — licensed electrical contractor EC13012832.
