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Dwelling Load Calculator

Run a standard NEC Article 220 dwelling load calculation to size a residential service.

General lighting and receptacles

NEC 220.41 assigns 3 VA per square foot of habitable floor area. Measure from the outside dimensions and exclude open porches, unfinished attics and unfinished basements not adaptable for use.

ft²

220.52(A) — two minimum, 1,500 VA each.

Cooking, laundry and fixed appliances

Enter nameplate ratings. Leave an appliance at zero if the dwelling does not have it. Four or more fastened-in-place appliances trigger the 75% demand factor in NEC 220.53.

kW

Table 220.55 Column C demand is applied. Zero for a gas range.

VA

220.54 — 5,000 VA minimum, or nameplate if higher.

VA
VA
VA
VA
VA

Wall oven, cooktop, attic fan, well pump, sump pump — total them here.

EV charging, pool and spa

These are not eligible for the 220.53 demand factor and are counted at full value.

A

220.57 counts EV supply equipment at nameplate or 7,200 VA, whichever is greater.

VA

Pump plus heater nameplate.

Heating and cooling

NEC 220.60 counts only the larger of two non-coincident loads, because heating and cooling do not run at the same time. Enter both and the calculation keeps the greater one.

VA

Furnace strip heat, baseboard, or heat pump auxiliary. Zero for gas heat.

VA

Compressor plus air handler nameplate.

What is on the house today, so the result can tell you whether it holds.

Recommended service

150 Aat 240 V

Calculated load is 35,950 VA, or 149.8 A.
Total calculated loadAfter all Article 220 demand factors
35,950 VA
Calculated currentTotal VA ÷ 240 V
149.8 A
Load on your existing service100 A service
150%
Headroom at the recommended sizeSpare capacity for future load
0.2 A

A 100 A service is not adequate

The calculated load of 149.8 A exceeds a 100 A service, and the standard method points to 150 A. Before committing to an upgrade, price the Article 220 Part IV optional method — it frequently yields a smaller calculated load — and look at load management under NEC 625.42 and Article 750, which can shed EV or water heater load rather than force a service change.

Non-coincident loads handled

Heating at 10,000 VA and cooling at 5,000 VA cannot run together, so NEC 220.60 counts only the larger — 10,000 VA from electric heating.
NEC Article 220 Part III standard method, line by line
LoadCode basisConnected VADemand factorCalculated VA
General lighting group after demand factorsTable 220.45 — 100 / 35 / 25%10,50053.6% net5,625
Electric rangeTable 220.55 Column C12,00067%8,000
Electric clothes dryer220.54 — 5,000 VA minimum5,000100%5,000
Water heater220.53 — fastened in place4,50075%3,375
Dishwasher220.53 — fastened in place1,20075%900
Disposal220.53 — fastened in place90075%675
Built-in microwave220.53 — fastened in place1,50075%1,125
Larger of heating or cooling — electric heating220.60 — non-coincident loads15,000Larger only10,000
Largest motor, additional 25%220.50 with 430.245,00025%1,250
Total calculated load35,950 VA
Inside the general lighting group
ComponentCode basisCalculationVA
General lighting and receptacles220.41 — 3 VA/ft²2,000 ft² × 36,000
Small-appliance circuits (2)220.52(A) — 1,500 VA each2 × 1,5003,000
Laundry branch circuit220.52(B) — 1,500 VA1 × 1,5001,500
First 3,000 VATable 220.45 demand factor3,000 VA × 100%3,000
3,001 through 120,000 VATable 220.45 demand factor7,500 VA × 35%2,625
General lighting group, calculated10,500 VA connected5,625 VA
Standard service sizes against this calculated load
Service sizeCapacity at 240 VLoad on serviceStatus
100 A24,000 VA150%Undersized
125 A30,000 VA120%Undersized
150 A36,000 VA100%Recommended
200 A48,000 VA75%Adequate
225 A54,000 VA67%Adequate
400 A96,000 VA37%Adequate

What this assumes

  • Uses the NEC Article 220 Part III standard method for a single dwelling unit.
  • General lighting load is 3 VA per square foot of habitable area, with Table 220.45 demand factors applied.
  • The larger of heating or cooling is counted, per NEC 220.60, since they do not run simultaneously.

Important

A service upgrade requires a permit, a utility coordination appointment and an inspection everywhere in the United States. Use this to understand the scope before you call — not to perform the work.

Understanding the result

Why 100 amps is often not enough anymore

A 100A service was sized for a house with gas heat, gas cooking and no air conditioning. Add a heat pump, an induction range, a heat pump water heater and a Level 2 EV charger and the calculated load routinely exceeds 100A, which is why panel upgrades have become one of the most common residential electrical jobs.

Standard method versus optional method

Article 220 Part III is the standard method used here. Part IV offers an optional method for dwellings that often yields a smaller calculated load by applying a single demand factor to the total connected load. Electricians commonly run both and use whichever legitimately produces the smaller service.

Load management as an alternative

NEC 625.42 and 750 permit energy management systems that shed load rather than forcing a service upgrade. A managed EV charger or a smart panel can frequently avoid a five-figure service upgrade, and is worth pricing before you commit.

Common questions

Do I need a 200 amp service?
It depends on your calculated load, not your house size. A 2,000 square foot home with gas heat and no EV often calculates under 100A. The same home with a heat pump, induction range and EV charger usually exceeds it.
Can I avoid a service upgrade for an EV charger?
Often yes. A load-managed charger, a lower charging amperage setting, or a smart panel that sheds other loads can keep you inside your existing service. The NEC explicitly allows these approaches.

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