Residential Service Load Calculation: A Worked Example for a 2,000 Square Foot House

A residential service load calculation is the math that decides whether a house gets a 150 A or 200 A service, and it shows up everywhere: new construction permits, service upgrades, and increasingly on EV charger and heat pump retrofits where the utility or AHJ wants proof the existing service has headroom. This post works the NEC Article 220 standard method line by line for a specific house, with every number shown.

The example house

Single-family, 2,000 square feet of habitable space. Electric range with a 12 kW nameplate. Electric dryer, 5.5 kW. Water heater, 4,500 W. Dishwasher, 1,200 W. Disposal, 900 W. Built-in microwave, 1,500 W. Electric furnace with 9.6 kW of strip heat, and a 3.5 kVA condensing unit for cooling. No EV charger yet, which is exactly why the headroom number at the end matters.

Step 1: general lighting and receptacle load

The standard method assigns 3 VA per square foot for general lighting and general-use receptacles: 2,000 x 3 = 6,000 VA. Add the required two small-appliance branch circuits at 1,500 VA each (3,000 VA) and the laundry circuit at 1,500 VA. Subtotal: 10,500 VA.

This bucket gets the lighting demand factors: the first 3,000 VA at 100 percent, the remainder at 35 percent. So 3,000 + (7,500 x 0.35) = 3,000 + 2,625 = 5,625 VA.

Step 2: the range

Household cooking equipment uses the demand factors of Table 220.55. For one range rated over 8.75 kW and not over 12 kW, Column C gives a demand of 8,000 VA, not the 12,000 nameplate. This table is generous by design, because nobody runs four burners, both ovens, and self-clean simultaneously. It is also the table people most often skip, which silently adds 4 kW to the calculation and bumps the service size for no reason.

Step 3: the dryer

Electric dryers count at the nameplate or 5,000 VA, whichever is larger. Our 5.5 kW dryer goes in at 5,500 VA. There is no demand reduction for a single dryer in a dwelling.

Step 4: fixed appliances

The fixed-appliance rule: when four or more fastened-in-place appliances are on the service (not counting the range, dryer, space heating, or AC), the group can be taken at 75 percent. We have four: water heater 4,500, dishwasher 1,200, disposal 900, microwave 1,500, totaling 8,100 VA. At 75 percent: 6,075 VA. With only three fixed appliances this group would ride at 100 percent, so the fourth appliance actually lowers the calculated total. The code is full of these small jokes.

Step 5: heating versus cooling

Heat and AC do not run at the same time, so NEC 220.60 takes the larger of the two noncoincident loads and drops the smaller. Strip heat at 9,600 VA versus the condenser at 3,500 VA: heating wins, 9,600 VA goes in the total and the AC disappears from the calculation. On a heat pump house the comparison is between the compressor-plus-supplemental-heat figure and cooling, and supplemental heat usually still wins.

Step 6: total it and convert to amps

Lighting and receptacles after demand: 5,625. Range: 8,000. Dryer: 5,500. Fixed appliances: 6,075. Heating: 9,600. Total: 34,800 VA.

At 240 V single-phase: 34,800 / 240 = 145 A. The minimum service that covers the calculated load is 150 A. The practical answer for new construction is a 200 A service anyway, because the cost difference at build time is small and the headroom question arrives later as a 48 A EV charger.

The EV charger follow-up everyone asks

With a 200 A service and this calculated load, the spare capacity is 200 – 145 = 55 A of calculated headroom. A 48 A level 2 charger is a continuous load and counts at 125 percent: 60 A, which does not fit on paper. The honest options: a 32 A charger (40 A calculated) fits cleanly; a load management device that throttles the charger lets the bigger unit comply; or rework the calculation with the optional method of 220.82, which frequently produces a lower total for all-electric houses and is worth running before anyone quotes a service upgrade. On the 150 A service, the spare 5 A means the charger conversation starts at “load management or upgrade,” and the calculation above is the document that proves it either way.

Notes on doing this for real

Use nameplates, not assumptions, for every fixed appliance; the 4,500 W water heater you assumed has a way of being a 5,500 W tankless booster in the field. Watch which code cycle the AHJ enforces, because table numbers occasionally move between editions even when the method does not. And keep the worked sheet, because the load calc that got the permit is the starting point for every future “can the panel take a hot tub” question on that house.

The free electrical load calculator on this site runs this same standard-method math from your square footage and appliance list, which is handy for the first pass before you commit the numbers to a permit form.