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    Calculates locally in your browser · NEC Article 220 dwelling load
    Electrical / service sizing

    Dwelling service load

    The standard method is a demand-factor calculation, not a sum: general lighting, small-appliance and laundry loads go through Table 220.42, which charges the first 3,000 VA at 100% and everything above it at 35%. Appliances have their own factors, and heating and cooling are counted once, not twice, because they never run together.

    Service200 AHeatingLargerCircuits2
    Service rating
    200 A
    184 A calculated at 240 V
    Demand load
    44,050 VA
    from 50,000 VA of nameplate
    Demand reduction
    12%
    removed by Table 220.42 and the appliance factors
    HVAC load
    12,000 VA
    heating governs
    The demand calculation
    Each line is a separate rule; the sum is the service load, not the sum of nameplates.
    200 A
    The demand calculation
    LineVARule
    General lighting6,0003 VA/ft², Table 220.12
    Lighting after demand4,050Table 220.42
    Small appliance3,0002 × 1,500 VA
    Laundry1,5001,500 VA
    Fixed appliances6,000100%, fewer than four
    Range8,000Table 220.55, from 12,000 VA
    Dryer5,0005,000 VA minimum, §220.54
    Water heater4,500100%
    HVAC12,000larger of heating and cooling, §220.60
    Total demand44,050the service load
    Service current184 Atotal ÷ 240 V
    Standard rating200 Anext size up, §240.6

    The demand factors remove 12% of the nameplate total. Sizing on the arithmetic sum would ask for 209 A instead of 184 A.

    Inspect the model
    Choose a quick result view, a scaled comparison, or the complete diagnostic set.
    Service current against floor area
    Only the lighting load scales with area, and after 3,000 VA it scales at 35% — so the curve flattens.
    Service current against floor area0.00043.0786.15129.22172.29215.371,000 ft²1,000 ft²1,500 ft²1,500 ft²2,000 ft²2,000 ft²2,500 ft²2,500 ft²3,000 ft²3,000 ft²4,000 ft²4,000 ft²Amps
    Where the load comes from
    HVAC and the range usually dominate; lighting is rarely the driver in a modern house.
    Where the load comes from0.0002832.005664.008496.001.133e+41.416e+4LightingLightingSmall app.Small app.AppliancesAppliancesRangeRangeDryerDryerWater ht.Water ht.HVACHVACVA
    Canonical equations
    The exact relationships implemented by this engine.

    3,000 + 35% of the next 117,000 + 25% above · Table 220.42.

    8 kW up to 12 kW, then +40% per kW · Table 220.55.

    max(heating, cooling) · §220.60 noncoincident.

    total VA ÷ 240 V · Then the next standard rating.

    engineering methodology

    A clear path from inputs to results.

    The standard method is a demand-factor calculation, not a sum: general lighting, small-appliance and laundry loads go through Table 220.42, which charges the first 3,000 VA at 100% and everything above it at 35%.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Enter the conditioned floor area and the small-appliance circuits.
    2. Add the fixed appliances, range, dryer and water heater.
    3. Enter both the heating and cooling loads.
    4. Read the demand load and the service rating.

    The formula

    L=3,000+0.35 (Llight−3,000)+…L = 3{,}000 + 0.35\,(L_{light} - 3{,}000) + \ldots

    Reference: NFPA 70 Article 220 Part III: Table 220.12, Table 220.42, §220.53, Table 220.55, §220.54 and §220.60.

    Worked example

    A 2,000 ft² house with electric range and heat pump

    Inputs
    • 2,000 ft², two small-appliance circuits, laundry.
    • 6,000 VA of fixed appliances, 12 kW range, 5 kW dryer, 4.5 kW water heater.
    • 6,000 VA cooling, 12,000 VA heating.
    Calculation path
    1. 1

      Lighting is 2,000 × 3 = 6,000 VA, which becomes 3,000 + 35% of 3,000 = 4,050 VA after demand.

    2. 2

      Small appliance and laundry add 4,500 VA, and the fixed appliances 6,000 VA.

    3. 3

      The 12 kW range counts as 8,000 VA under Table 220.55, and the dryer at 5,000 VA.

    4. 4

      Heating is larger than cooling, so 12,000 VA is counted once.

    5. 5

      The total is 44,050 VA, which is 183.5 A at 240 V — a 200 A service.

    Result

    44,050 VA · 183.5 A · 200 A service.

    Interpreting the result

    The demand factors remove about 12% here, and much more in a house with a large connected load. Sizing on the arithmetic sum of nameplates is the standard error: it can ask for a 400 A service where 200 A is correct, and the customer pays for the difference.

    Assumptions & limitations

    • The standard method of Article 220 Part III for a one-family dwelling.
    • General lighting at 3 VA/ft² for the whole conditioned area.
    • Heating and cooling are noncoincident, so only the larger counts.
    • No largest-motor adder, EV charging or pool.

    Frequently asked questions

    Why not just add the nameplates?

    Because the code recognises that not everything runs at once. The demand factors are the codified version of that, and using them is not optional if you want the service to be correctly sized.

    Does the range really count as 8 kW?

    For a 12 kW range, yes — Table 220.55 is generous. Above 12 kW you add 40% of the excess in whole kilowatts.

    Does an EV charger change this?

    Substantially. A 48 A charger adds 11,520 VA at 240 V and is usually continuous, so it is taken at 125%.

    What is the Optional Method?

    §220.82 gives a shorter calculation for a dwelling with a large connected load, and often produces a smaller service. It is an alternative, not a supplement.

    Do I add 25% for the largest motor?

    Yes, under §220.50 and §430.24, and it is a separate line this model does not include. It matters on a house with a large well pump or compressor.

    Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.