Residential Load Calculation (NEC 220.82)
- Code basis
- NEC 2023, Art. 220
- Editions
- 2017, 2020, 2023
- Methods
- 220.82 optional, 220.83 existing
- Service sizes
- 100 – 400 A
- EV charging
- 220.57 minimum, EMS-limited output
Method
Both are optional calculations. They differ in which loads are counted and in the size of the first tranche taken at full value.
Dwelling
Floor area is the area of habitable space, excluding open porches, garages and unfinished space not adaptable for use.
Appliances
Fastened-in-place and permanently connected equipment at nameplate. The ratings shown are examples; enter what is on the label.
Appliance 1
Read it from the equipment label.
Appliance 2
Read it from the equipment label.
Appliance 3
Read it from the equipment label.
Heating and cooling
Enter every system present. Only the largest single item is added, because heating and cooling are not expected to run together.
EV supply equipment
From the 2023 edition the load is the larger of the nameplate and a 7200 VA minimum. Earlier editions have no such floor.
Recommended service
Adequate125 A
Calculated load is 103.3 A at 240 V.
- Total calculated load
- 24,800 VA103.3 A at 240 V
- General load after demand factor
- 19,040 VAfrom 32,600 VA connected
- Heating or cooling added
- 5,760 VAair conditioning at 100 percent
- Headroom on existing service
- —no rating entered
- Result of the optional calculation only. The standard calculation is permitted for the same dwelling and can produce a different number, and some jurisdictions require it.
- A dwelling service is never smaller than 100 A. Size the service conductors from the selected rating, not from the calculated amperes.
Itemised calculation
| Step | Basis | Effect | Value |
|---|---|---|---|
| General lighting, 2200 sq ft at 3 VA per sq ft | 220.82 | — | 6600 VA |
| 3 small-appliance and laundry circuits at 1500 VA each | 220.82 | — | 11100 VA |
| 3 appliance nameplate ratings | 220.82 | — | 32600 VA |
| First 10,000 VA at 100 percent | 220.82 | cap 10000 | 10000 VA |
| Remaining 22,600 VA at 40 percent | 220.82 | × 0.4 | 19040 VA |
| Largest heating or cooling item: air conditioning at 100 percentGoverning | 220.82 | — | 24800 VA |
Each row carries the running total, not the item on its own, so the arithmetic can be followed straight down the column.
Heating and cooling selection
| Item and percentage | VA | Added |
|---|---|---|
| Air conditioning at 100 percent | 5,760 | Selected |
Only the largest item is added. A reviewer needs to see the full list to confirm the selection was made from it, which is why every candidate is shown rather than only the winner.
Calculated against the NEC 2023 edition using 220.82, 220.83. Confirm the edition adopted by your AHJ, which may differ and may carry local amendments.
Not covered by this tool
- The standard calculation, which is permitted for the same dwelling, applies its own demand factors to lighting, appliances, dryers and cooking equipment, and can return a different result.
- Multifamily and two-dwelling calculations, and the optional calculation for a multifamily building.
- Existing loads determined from a year of recorded demand data, which is a separate permitted method.
- Service conductor and service disconnect sizing, including the reduced ampacity permitted for dwelling service conductors.
- Panelboard bus rating, physical space for new circuits, and the busbar limits that apply where solar is present.
- Load management systems other than one limiting EV supply equipment.
- Generator, transfer switch and energy storage sizing.
Data last verified
Calculation Method
Six steps, in the order the code applies them.
Step 1
General lighting
Floor area at 3 VA per square foot. Covers general lighting and general-use receptacles, so neither is counted again.
Step 2
Branch circuits
1500 VA for each small-appliance and laundry branch circuit. Two small-appliance circuits is the minimum for a dwelling.
Step 3
Appliances at nameplate
Every fastened-in-place and permanently connected appliance at its nameplate rating, summed at full value. Range, water heater, dryer, dishwasher, disposer, well pump.
Step 4
Demand factor
The first 10,000 VA of that total at 100 percent and everything above it at 40 percent. The existing-dwelling method uses an 8,000 VA first tranche instead.
Step 5
Largest heating or cooling item
Added after the demand factor and never reduced by it. Only one item is added, because heating and cooling do not run together.
Step 6
Service size
Total volt-amperes divided by the service voltage, then rounded up to the next standard rating. A dwelling service is never smaller than 100 A.
The demand factor applies to the general load and the appliances only. The heating or cooling item is added after it at full value, and adding it before the demand factor understates the service by a wide margin.
Optional Method vs Existing Dwelling
Both are optional calculations. They differ in the size of the tranche taken at full value, and therefore in the answer.
| Item | New dwelling | Existing dwelling |
|---|---|---|
| First tranche at 100 percent | 10,000 VA | 8,000 VA |
| Remainder | 40 percent | 40 percent |
| Applies to | A dwelling served at 100 A or more | Adding load to a dwelling already served |
| Typical use | New construction, whole-house rewire, service upgrade | EV charger, heat pump, addition, ADU on an existing panel |
| Heating and cooling | Largest single item, added after the demand factor | Largest single item, added after the demand factor |
Unit Loads and Demand Factors
What each item contributes, and whether the demand factor reaches it.
| Load | Counted as | Factor |
|---|---|---|
| General lighting and general-use receptacles | 3 VA per sq ft | 100 percent, then the demand factor |
| Small-appliance branch circuit | 1500 VA each | 100 percent, then the demand factor |
| Laundry branch circuit | 1500 VA each | 100 percent, then the demand factor |
| Fastened-in-place appliance | Nameplate | 100 percent, then the demand factor |
| EV supply equipment, 2023 edition | Greater of nameplate and 7,200 VA | 100 percent, then the demand factor |
| Air conditioning | Nameplate | 100 percent, no demand factor |
| Heat pump without supplemental heat | Compressor nameplate | 100 percent, no demand factor |
| Heat pump with supplemental heat | Compressor plus supplemental heat | 100 percent plus 65 percent |
| Electric space heating, fewer than four units | Nameplate | 65 percent |
| Electric space heating, 4 or more separately controlled units | Nameplate | 40 percent |
| Electric thermal storage | Nameplate | 100 percent, no demand factor |
Service Size by Calculated Load
Standard residential ratings and the calculated load each one covers at 240 V.
| Service | Maximum VA | Calculated load covered |
|---|---|---|
| 100 A | 24,000 | Up to 24,000 VA |
| 125 A | 30,000 | 24,001 – 30,000 VA |
| 150 A | 36,000 | 30,001 – 36,000 VA |
| 200 A | 48,000 | 36,001 – 48,000 VA |
| 225 A | 54,000 | 48,001 – 54,000 VA |
| 300 A | 72,000 | 54,001 – 72,000 VA |
| 400 A | 96,000 | 72,001 – 96,000 VA |
When This Calculation Is Required
The permit questions this calculation exists to answer.
| Situation | What it decides | Basis |
|---|---|---|
| 40 A EV charger on a 1970s house with a 100 A service | Whether the service has to be upgraded | Run the existing-dwelling method. This is the single most common reason a dwelling load calculation gets filed. |
| Gas furnace replaced by an air-source heat pump | Which heating or cooling item now governs | The compressor plus strip heat usually beats the old air conditioner, and the increase lands after the demand factor. |
| New 3200 sq ft dwelling with an electric range and dryer | 200 A or 400 A service | Floor area drives the general load, but the appliance total is what pushes the remainder into the 40 percent band. |
| Accessory dwelling unit added over a garage | Whether the existing service can carry both | Treated as added load on the existing dwelling unless it is separately metered and served. |
| Two EV chargers with an energy management system | Whether the nameplate or the limited output is counted | A listed system that limits the charging current lets the equipment be counted at its limited output, which frequently avoids an upgrade. |
| Panel change with no new load | Nothing, on its own | A calculation is still typically required for the permit, and it is the point at which an undersized existing service surfaces. |
Reading the Result
What to do with each of the five outcomes this calculation produces.
The calculated load just exceeds the existing service
Look at the EV supply equipment first. A listed energy management system that limits the charging current lets the equipment be counted at the limited output rather than its nameplate, and that alone often brings a 100 A service back into range.
The optional method returns a larger service than expected
Run the standard calculation. It applies separate demand factors to lighting, dryers and cooking equipment, and for a dwelling with a large range and little else it can return a smaller result. Either method is permitted; use the one that fits the installation.
Heating and cooling are both large
Only the largest item is added, so oversizing the air conditioner has no effect once the heating item exceeds it. Verify which one the calculation selected before spending money on equipment to change the result.
The result lands between two standard sizes
Round up. Then check the panelboard: a 200 A service needs a bus rated for it and physical space for the new circuits, and neither is part of this calculation.
The service is being upgraded anyway
Size for the load you expect within the life of the service, not the load today. A second EV, a heat pump conversion and a range swap are each a substantial addition, and the incremental cost at the time of the upgrade is far lower than a second upgrade later.