Generac Size Calculator

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Generator Sizing Inputs

Recommended Generator Size

Understanding Your Generac Generator Size Needs

Choosing the right size Generac generator is crucial for ensuring you have reliable backup power when you need it most. A generator that’s too small might not be able to handle your essential loads, leaving you without power for critical appliances. Conversely, an oversized generator can be unnecessarily expensive to purchase and operate, and may not run as efficiently.

This calculator provides a general recommendation based on several key factors. It aims to help you estimate the continuous wattage your home will require during a power outage.

How the Calculation Works:

Our calculator uses a simplified approach to estimate your backup power needs. It considers the following:

• Home Size (sq ft): Larger homes generally have more appliances and higher overall energy demands. A baseline wattage is estimated based on square footage.
• Major Appliances: Appliances like refrigerators, air conditioners, ovens, and well pumps have high starting (surge) and running (continuous) wattage requirements. Each is assigned a typical wattage value.
• Common Appliances: Items like televisions, computers, lighting, and small kitchen appliances contribute to the overall load.
• Critical Appliances: Specialized equipment or essential systems (like medical devices or sump pumps) are given priority and added to the total load.
• Power Outage Frequency: While not directly in the wattage calculation, this factor influences the recommendation for reliability and potential upgrade paths, suggesting larger units for areas with more frequent outages.

Estimating Wattage:

The calculator applies estimated wattage figures for each category. These are general approximations:

• Home Size: A base wattage is calculated, often around 10-15 watts per square foot, but this can vary significantly.
• Major Appliances:
  • Refrigerator: ~200 running watts, ~1000 surge watts
  • Central Air Conditioner: ~1500-5000 running watts, ~2-3x surge
  • Electric Oven: ~2000-4000 running watts, minimal surge
  • Well Pump: ~1000 running watts, ~2000-3000 surge watts
• Common Appliances:
  • Lights (LED): ~10-20 watts
  • Lights (Incandescent): ~60-100 watts
  • Television: ~100-300 watts
  • Computer: ~150-300 watts
  • Microwave: ~800-1500 watts
• Critical Appliances: Wattage is assumed to be provided by the user or a standard higher value if unspecified.

The calculator sums the running watts of all appliances and adds the surge watts for the single largest surge appliance. This provides an estimated total wattage needed.

Interpreting the Results:

The output will be a recommended generator size in watts (W) or kilowatts (kW). Generac offers a range of portable and standby generators to meet these needs. It’s always advisable to consult with a qualified electrician or Generac dealer to finalize your decision, as your specific appliance models and home wiring can influence the exact requirements.

Disclaimer: This calculator provides an estimated recommendation only. Actual power needs may vary. Always consult with a professional for precise sizing and installation.

function calculateGeneracSize() {
// Get input values
var homeSize = parseFloat(document.getElementById(“homeSize”).value);
var majorAppliancesCount = parseInt(document.getElementById(“majorAppliances”).value);
var commonAppliancesCount = parseInt(document.getElementById(“commonAppliances”).value);
var powerOutageFrequency = document.getElementById(“powerOutageFrequency”).value;
var criticalAppliancesText = document.getElementById(“criticalAppliances”).value.trim();

var resultElement = document.getElementById(“result”);

// — Input Validation —
if (isNaN(homeSize) || homeSize <= 0) {
resultElement.textContent = "Please enter a valid home size.";
return;
}
if (isNaN(majorAppliancesCount) || majorAppliancesCount < 0) {
resultElement.textContent = "Please enter a valid number for major appliances.";
return;
}
if (isNaN(commonAppliancesCount) || commonAppliancesCount item.trim() !== ”);
if (criticalAppliancesList.length > 0) {
// Assign a higher average wattage for critical items, adjust as needed
var criticalApplianceEstimatedWatts = 2000; // A conservative estimate
totalRunningWatts += criticalAppliancesList.length * criticalApplianceEstimatedWatts;
maxSurgeWatts = Math.max(maxSurgeWatts, criticalApplianceEstimatedWatts * 1.5); // Assume surge potential
}

// — Refine Surge Calculation —
// The total required wattage is the sum of running watts PLUS the *difference* needed for the single largest surge.
// However, a simpler approach for recommendation is to take the higher of:
// a) Total running watts
// b) The largest surge wattage PLUS the running watts of everything else (which is complex to isolate here)
// For a recommendation, we’ll use total running watts + a buffer for surges, or a higher threshold if critical appliances demand it.
var calculatedTotalWatts = totalRunningWatts + maxSurgeWatts; // A simplified way to ensure surge capacity is considered

// — Determine Recommended Size Bracket —
var recommendedSize = 0;
if (calculatedTotalWatts <= 3500) {
recommendedSize = 3500; // Smallest common size for basic needs
} else if (calculatedTotalWatts <= 5000) {
recommendedSize = 5000;
} else if (calculatedTotalAESWats <= 7500) {
recommendedSize = 7500;
} else if (calculatedTotalAESWats <= 10000) {
recommendedSize = 10000;
} else if (calculatedTotalAESWats <= 15000) {
recommendedSize = 15000;
} else if (calculatedTotalAESWats 0) {
var resultText = recommendedSize.toLocaleString() + ” Watts (” + (recommendedSize / 1000).toLocaleString(undefined, {minimumFractionDigits: 1, maximumFractionDigits: 1}) + ” kW)”;
if (criticalAppliancesList.length > 0 || powerOutageFrequency === “frequently”) {
resultText += “Consider a whole-home standby generator for critical needs.“;
}
resultText += “” + frequencyRecommendation + ““;
resultElement.innerHTML = resultText;
} else {
resultElement.textContent = “Could not determine a recommended size. Please check your inputs.”;
}
}