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Dwelling load calculation

Updated · Written for the 2023 NEC

Short answer

A dwelling load calculation adds up the minimum loads that Article 220 of the 2023 NEC assigns to a house, applies the allowed demand factors, and divides the total by the service voltage to size the service. Under the standard method you take 3 VA per square foot for general lighting (220.41), add 1,500 VA for each small-appliance and laundry circuit (220.52), reduce that group with Table 220.45, then add fixed appliances, the dryer, the range, and the larger of heat or air conditioning.

What a dwelling load calculation is

A dwelling load calculation is a code-minimum estimate of the demand a house will place on its service or feeder. It is not a count of everything connected. The NEC knows that every light, appliance, and heater will not run at full load at the same time, so Article 220 lets you reduce several loads with demand factors.

The exam tests this heavily because it combines many small rules into one long problem. If you can work the standard method from start to finish without skipping a step, most single-rule questions become easy. For more math practice, see the exam calculations guide.

The key rules (with NEC sections)

  • General lighting, 220.41. Use 3 VA per square foot of floor area. Floor area is measured from the outside dimensions (220.5(C)) and leaves out open porches and unfinished spaces that cannot be used later as living space. This load also covers the general-use receptacles, so you do not add 180 VA per receptacle in a dwelling.
  • Small-appliance circuits, 220.52(A). Add 1,500 VA for each 20-ampere small-appliance branch circuit. A house needs at least two, and every extra one also counts 1,500 VA.
  • Laundry circuit, 220.52(B). Add 1,500 VA for the laundry branch circuit.
  • Lighting demand factors, Table 220.45. The lighting, small-appliance, and laundry loads are combined and reduced together. For dwellings, the first 3,000 VA counts at 100%, the portion from 3,001 to 120,000 VA counts at 35%, and anything above 120,000 VA counts at 25%.
  • Fastened-in-place appliances, 220.53. Water heaters, dishwashers, disposals, built-in microwaves, and similar appliances count at 75% when there are four or more of them. With three or fewer, they count at 100%. Ranges, dryers, space heating, air conditioning, and EV chargers are not part of this group.
  • Clothes dryers, 220.54. Use 5,000 VA or the nameplate rating, whichever is larger.
  • Ranges and cooking appliances, 220.55. A single range rated 12 kW or less counts at 8 kW using Column C of Table 220.55. For each kW (or major fraction) over 12 kW, increase the 8 kW by 5% (Note 1).
  • Fixed space heating, 220.51. Count it at 100% of the connected load.
  • Noncoincident loads, 220.60. Heating and air conditioning that will not run at the same time are not added together. Use only the larger one.
  • Motors, 220.50. Include 25% of the largest motor in the calculation, following the motor rules of Article 430. See motor circuits.
  • EV chargers, 220.57. New in 2023: count EVSE at 7,200 W or the nameplate rating, whichever is larger.

How to calculate it, step by step

General lighting = sq ft × 3 VA
Lighting group = general lighting + (1,500 VA × small-appliance circuits) + 1,500 VA laundry
Net lighting group = 3,000 VA + (lighting group − 3,000 VA) × 35%
Service amperes = total VA ÷ 240 V

After the lighting group, add the fastened-in-place appliances, dryer, range, the larger of heat or cooling, and 25% of the largest motor. Divide by 240 V and pick a service rating at or above that current. A one-family dwelling service must be at least 100 amperes (230.79(C)).

Worked example

A one-family dwelling measures 2,500 sq ft from outside dimensions. It has two small-appliance circuits, one laundry circuit, a 12 kW range, a 5.5 kW dryer, a 4,500 VA water heater, a 1,200 VA dishwasher, an 800 VA disposal, and a 1,300 VA built-in microwave. It has 10 kW of electric heat (including its blower) and a 6 kVA air conditioner that never run at the same time. The service is 120/240 volts.

  1. General lighting: 2,500 × 3 = 7,500 VA.
  2. Add small-appliance and laundry circuits: 7,500 + 3,000 + 1,500 = 12,000 VA.
  3. Demand factors: the first 3,000 VA at 100% is 3,000 VA. The remaining 9,000 VA at 35% is 3,150 VA. Net lighting group = 6,150 VA.
  4. Fastened-in-place appliances: 4,500 + 1,200 + 800 + 1,300 = 7,800 VA. There are four, so take 75%: 5,850 VA.
  5. Dryer: the nameplate of 5,500 VA is larger than 5,000 VA, so use 5,500 VA.
  6. Range: 12 kW is not over 12 kW, so Column C gives 8,000 VA.
  7. Heat or air conditioning: 10,000 VA of heat is larger than 6,000 VA of cooling, so use 10,000 VA.
  8. Largest motor: with the air conditioner dropped, the largest remaining motor is the 800 VA disposal. 25% of 800 VA = 200 VA.
  9. Total: 6,150 + 5,850 + 5,500 + 8,000 + 10,000 + 200 = 35,700 VA.
  10. Current: 35,700 ÷ 240 = 148.75 A. The minimum service is 150 A.

Range over 12 kW. A single 16 kW range is 4 kW over 12 kW. 4 × 5% = 20%, so the demand is 8 kW × 1.20 = 9.6 kW.

For a one-family dwelling at 120/240 volts, 310.12 lets the service conductors be sized at 83% of the service rating. Conductor sizing is covered on the conductor ampacity and services and feeders pages.

Common exam mistakes

  • Forgetting the appliance circuits in the demand step. The 1,500 VA circuits go into the lighting total before Table 220.45, not after it.
  • Applying 35% to everything. Only the portion above the first 3,000 VA gets 35%.
  • Using 75% for three appliances. The 220.53 demand factor needs four or more fastened-in-place appliances.
  • Using the dryer nameplate when it is below 5,000 VA. The minimum is 5,000 VA under 220.54.
  • Adding heat and air conditioning together. Under 220.60 you use only the larger noncoincident load.
  • Adding 180 VA per receptacle. That rule is for other than dwelling units. In a house, general-use receptacles are inside the 3 VA per sq ft.
  • Mixing up the methods. The optional method of 220.82 uses different percentages (first 10 kVA at 100%, remainder at 40%). Read which method the question asks for.

Practice questions

Question 1 · Load calculationsA 3,000 sq ft dwelling has two small-appliance circuits and one laundry circuit. What is the net general lighting and appliance-circuit load after demand factors?
Show answer

Answer: D. 6,675 VA. NEC Table 220.45

General lighting is 3,000 × 3 = 9,000 VA, plus 4,500 VA for the small-appliance and laundry circuits, for 13,500 VA. First 3,000 VA at 100% plus 10,500 VA at 35% (3,675 VA) gives 6,675 VA.

  1. 3,000 ft² × 3 = 9,000 VA; + 4,500 VA = 13,500 VA
  2. First 3,000 VA @ 100% = 3,000 VA
  3. 10,500 VA @ 35% = 3,675 VA
  4. Net = 6,675 VA
Question 2 · Load calculationsA dwelling's electric clothes dryer is rated 4.5 kW. What load must be used for it in the standard calculation?
Show answer

Answer: B. 5,000 VA. NEC 220.54

The dryer load is 5,000 VA or the nameplate rating, whichever is larger. Since 4,500 VA is less than 5,000 VA, use 5,000 VA.

  1. Nameplate = 4,500 VA
  2. Minimum = 5,000 VA
  3. Use larger = 5,000 VA
Question 3 · Load calculationsWhat is the demand load for one 14 kW household range?
Show answer

Answer: A. 8.8 kW. NEC Table 220.55

Note 1 to Table 220.55 increases Column C by 5% for each kW over 12 kW. 14 kW is 2 kW over, so 8 kW × 1.10 = 8.8 kW.

  1. 14 − 12 = 2 kW over
  2. 2 × 5% = 10% increase
  3. 8 kW × 1.10 = 8.8 kW
Question 4 · Load calculationsA dwelling has four fastened-in-place appliances: 1,200 VA dishwasher, 900 VA disposal, 4,500 VA water heater, and 1,500 VA built-in microwave. What is their demand load?
Show answer

Answer: D. 6,075 VA. NEC 220.53

Four or more fastened-in-place appliances (other than ranges, dryers, heating, and A/C) may be calculated at 75%. 1,200 + 900 + 4,500 + 1,500 = 8,100 VA × 0.75 = 6,075 VA.

  1. Total = 1,200 + 900 + 4,500 + 1,500 = 8,100 VA
  2. Four appliances → 75%
  3. 8,100 × 0.75 = 6,075 VA
Question 5 · Load calculationsA 2,000 sq ft dwelling has a 12 kW range, 5 kW dryer, 4.5 kW water heater, 1.2 kW dishwasher, 0.8 kW disposal, 8 kW electric heat, and a 5 kVA A/C unit. Using the standard method, what is the calculated service load in amperes at 240 volts? The 800 VA disposal is the largest motor remaining in the calculation; the dishwasher motor is smaller. The heating and cooling loads are noncoincident, and the 8 kW heating load includes its blower. Include the required motor allowance.
Show answer

Answer: A. 139 A. NEC Table 220.45; 220.50; 220.53; 220.54; Table 220.55; 220.60

After dwelling demand factors, lighting and the required small-appliance and laundry circuits contribute 5,625 VA. Add the three fixed appliances at 6,500 VA, dryer at 5,000 VA, range at 8,000 VA, and the larger heating allowance at 8,000 VA; add 25% of the 800 VA disposal motor. The resulting 33,325 VA divided by 240 V is approximately 139 A.

  1. Lighting and required circuits: 2,000 × 3 + 4,500 = 10,500 VA.
  2. Dwelling demand: 3,000 + 7,500 × 0.35 = 5,625 VA.
  3. Fixed appliances: 4,500 + 1,200 + 800 = 6,500 VA; three appliances receive no 75% demand.
  4. Dryer 5,000 VA; range 8,000 VA; noncoincident heating allowance 8,000 VA.
  5. Largest remaining motor allowance: 800 × 0.25 = 200 VA.
  6. Total = 5,625 + 6,500 + 5,000 + 8,000 + 8,000 + 200 = 33,325 VA.
  7. Current = 33,325 / 240 = 138.85 A, approximately 139 A.

Try a full set of mixed questions on the practice test.

Frequently asked questions

How many VA per square foot is a dwelling unit?

A dwelling unit is calculated at 3 VA per square foot for general lighting and general-use receptacles under 220.41 of the 2023 NEC. Measure the floor area from the outside dimensions.

What are the dwelling demand factors for general lighting?

Table 220.45 takes the first 3,000 VA at 100%, the next portion up to 120,000 VA at 35%, and anything over 120,000 VA at 25%. The small-appliance and laundry circuit loads are included in the total before these factors are applied.

Was 220.12 renumbered in the 2023 NEC?

Yes. In the 2023 NEC the dwelling general lighting unit load is in 220.41, and the lighting demand factors are in Table 220.45. Older study material may still cite 220.12 and Table 220.42, so check which edition your exam uses.

What is the difference between the standard and optional methods?

The standard method applies separate demand factors to each type of load. The optional method in 220.82 adds most loads at nameplate, takes the first 10 kVA at 100% and the rest at 40%, then adds heating or cooling at its own percentages.

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