Home Occupancy Load Calculator

ANA›Life Services Authority›National Calculator Authority›Home Occupancy Load Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Home Occupancy Load Calculator

Estimate the total electrical occupancy load for a residential home using the NEC (National Electrical Code) general lighting load method plus major appliance loads.

Total Finished Floor Area (sq ft)

Number of Small Appliance Branch Circuits

NEC minimum is 2 circuits (1500 VA each)

Number of Laundry Branch Circuits

NEC minimum is 1 circuit (1500 VA each)

Electric Range / Oven Load (watts, 0 if none)

Electric Dryer Load (watts, 0 if none)

Air Conditioning Load (watts, 0 if none)

Electric Heat Load (watts, 0 if none)

Electric Water Heater (watts, 0 if none)

Service Voltage (volts)

240V (Standard US Residential) 120V (Single Phase) 208V (Some Multi-family)

Calculate Occupancy Load

function homCalc() { var resultDiv = document.getElementById('hom-result'); resultDiv.style.display = 'block'; resultDiv.className = 'calc-result';

// --- Gather Inputs --- var floorArea = parseFloat(document.getElementById('hom-floor-area').value); var smallAppliance = parseFloat(document.getElementById('hom-small-appliance').value); var laundry = parseFloat(document.getElementById('hom-laundry').value); var rangeW = parseFloat(document.getElementById('hom-range').value) || 0; var dryerW = parseFloat(document.getElementById('hom-dryer').value) || 0; var acW = parseFloat(document.getElementById('hom-ac').value) || 0; var heatW = parseFloat(document.getElementById('hom-heat').value) || 0; var waterHeaterW = parseFloat(document.getElementById('hom-water-heater').value) || 0; var voltage = parseFloat(document.getElementById('hom-voltage').value);

// --- Validation --- var errors = []; if (isNaN(floorArea) || floorArea 20000) errors.push("Floor area must be between 100 and 20,000 sq ft."); if (isNaN(smallAppliance) || smallAppliance 20 || !Number.isInteger(smallAppliance)) errors.push("Small appliance circuits must be a whole number between 2 and 20 (NEC minimum is 2)."); if (isNaN(laundry) || laundry 5 || !Number.isInteger(laundry)) errors.push("Laundry circuits must be a whole number between 1 and 5 (NEC minimum is 1)."); if (rangeW 30000) errors.push("Range/oven load must be between 0 and 30,000 watts."); if (dryerW 15000) errors.push("Dryer load must be between 0 and 15,000 watts."); if (acW 30000) errors.push("AC load must be between 0 and 30,000 watts."); if (heatW 50000) errors.push("Heat load must be between 0 and 50,000 watts."); if (waterHeaterW 12000) errors.push("Water heater load must be between 0 and 12,000 watts.");

if (errors.length > 0) { resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = 'Please fix the following errors:' + errors.map(function(e){ return ''; }).join('') + ''; return; }

// ===================================================================== // NEC Article 220 — Residential Load Calculation (Standard Method) // =====================================================================

// STEP 1: General Lighting Load // NEC 220.12: 3 VA per sq ft for dwelling units var lightingVA = floorArea * 3;

// STEP 2: Small Appliance Branch Circuits // NEC 220.52(A): 1500 VA per circuit var smallApplianceVA = smallAppliance * 1500;

// STEP 3: Laundry Branch Circuit(s) // NEC 220.52(B): 1500 VA per circuit var laundryVA = laundry * 1500;

// STEP 4: Subtotal before demand factors var subtotalVA = lightingVA + smallApplianceVA + laundryVA;

// STEP 5: Apply NEC Demand Factors (Table 220.42) // First 3000 VA @ 100% // Next 3001–120,000 VA @ 35% // Remainder over 120,000 VA @ 25% var demandVA = 0; if (subtotalVA 12 kW: add 400 W per kW above 12 kW var rangeDemandVA = 0; if (rangeW > 0) { if (rangeW 0) { dryerDemandVA = Math.max(dryerW, 5000); }

// STEP 8: Heating vs. AC — use the larger (NEC 220.60, non-coincident loads) var hvacDemandVA = Math.max(acW, heatW);

// STEP 9: Water Heater (100% of nameplate) var waterHeaterVA = waterHeaterW;

// STEP 10: Total Calculated Load var totalVA = demandVA + rangeDemandVA + dryerDemandVA + hvacDemandVA + waterHeaterVA;

// STEP 11: Service Amperage Required // I = VA / V (single-phase 240V service: I = VA / 240) var serviceAmps = totalVA / voltage;

// STEP 12: Recommended Service Size (round up to standard breaker sizes) var standardSizes = [100, 125, 150, 200, 225, 300, 400, 600]; var recommendedService = standardSizes[standardSizes.length - 1]; for (var i = 0; i '; html += 'Load ComponentVAWatts';

function row(label, va, note) { return '' + '' + label + (note ? '' + note + '' : '') + '' + '' + va.toLocaleString(undefined,{maximumFractionDigits:0}) + '' + '' + va.toLocaleString(undefined,{maximumFractionDigits:0}) + '' + ''; }

html += row('General Lighting (3 VA × ' + floorArea.toLocaleString() + ' sq ft)', lightingVA, 'NEC 220.12'); html += row('Small Appliance Circuits (' + smallAppliance + ' × 1,500 VA)', smallApplianceVA, 'NEC 220.52(A)'); html += row('Laundry Circuit(s) (' + laundry + ' × 1,500 VA)', laundryVA, 'NEC 220.52(B)'); html += 'Subtotal (before demand factors)' + subtotalVA.toLocaleString(undefined,{maximumFractionDigits:0}) + '' + subtotalVA.toLocaleString(undefined,{maximumFractionDigits:0}) + ''; html += 'After Demand Factors Applied' + demandVA.toLocaleString(undefined,{maximumFractionDigits:0}) + '' + demandVA.toLocaleString(undefined,{maximumFractionDigits:0}) + '';

if (rangeDemandVA > 0) html += row('Electric Range/Oven Demand', rangeDemandVA, 'NEC Table 220.55 — single range demand'); if (dryerDemandVA > 0) html += row('Electric Dryer Demand', dryerDemandVA, 'NEC 220.54 — min 5,000 W or nameplate'); if (hvacDemandVA > 0) { var hvacLabel = (acW >= heatW) ? 'Air Conditioning (larger of AC vs Heat)' : 'Electric Heat (larger of AC vs Heat)'; html += row(hvacLabel, hvacDemandVA, 'NEC 220.60 — non-coincident loads, use larger'); } if (waterHeaterVA > 0) html += row('Electric Water Heater', waterHeaterVA, '100% of nameplate rating');

html += '';

html += ''; html += ''; html += 'Total Calculated Load' + totalKVA.toFixed(2) + ' kVA'; html += 'Minimum Service Amperage' + serviceAmps.toFixed(1) + ' A'; html += 'Recommended Service Size' + recommendedService + ' A'; html += 'Service Voltage' + voltage + ' V'; html += '';

// Demand factor breakdown note var df1 = Math.min(subtotalVA, 3000); var df2 = subtotalVA > 3000 ? Math.min(subtotalVA, 120000) - 3000 : 0; var df3 = subtotalVA > 120000 ? subtotalVA - 120000 : 0; html += ''; html += 'Demand Factor Breakdown (NEC Table 220.42):'; html += 'First 3,000 VA @ 100% = ' + (df1 * 1.00).toLocaleString(undefined,{maximumFractionDigits:0}) + ' VA'; if (df2 > 0) html += 'Next ' + df2.toLocaleString() + ' VA (3,001–120,000) @ 35% = ' + (df2 * 0.35).toLocaleString(undefined,{maximumFractionDigits:0}) + ' VA'; if (df3 > 0) html += 'Remainder ' + df3.toLocaleString() + ' VA (>120,000) @ 25% = ' + (df3 * 0.25).toLocaleString(undefined,{maximumFractionDigits:0}) + ' VA'; html += 'Demand-adjusted subtotal = ' + demandVA.toLocaleString(undefined,{maximumFractionDigits:0}) + ' VA'; html += '';

resultDiv.innerHTML = html; }

#### Formula & Method

This calculator uses the NEC Article 220 Standard Method for residential load calculations:

General Lighting Load: Floor Area (sq ft) × 3 VA/sq ft (NEC 220.12)
Small Appliance Circuits: Number of Circuits × 1,500 VA (NEC 220.52(A), minimum 2)
Laundry Circuit(s): Number of Circuits × 1,500 VA (NEC 220.52(B), minimum 1)
Demand Factors applied to subtotal (NEC Table 220.42):
Electric Range: Single range ≤12 kW = 8,000 W demand; >12 kW add 400 W per kW above 12 kW (NEC Table 220.55, Column C)
Electric Dryer: max(nameplate, 5,000 W) (NEC 220.54)
HVAC: Larger of AC or Heat load (non-coincident) (NEC 220.60)
Water Heater: 100% of nameplate rating
Service Amps: Total VA ÷ Voltage

#### Assumptions & References

Calculations follow NFPA 70: National Electrical Code (NEC) 2023, Article 220 — Branch-Circuit, Feeder, and Service Load Calculations.

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