When power outages strike, having a properly sized generator can make the difference between minor inconvenience and major disruption. Let’s explore what size generator you need to keep your home running smoothly during outages.

Understanding Generator Sizing Basics

Generator capacity is measured in watts (W) or kilowatts (kW), where 1,000 watts equals 1 kilowatt. The size you need depends on:

• Home square footage
• Number of appliances you want to power
• Regional climate (heating/cooling needs)
• Your electrical panel capacity

Common Generator Size Categories

Small Portable Generators (3,000-5,000 watts)

These can power:

• Refrigerator
• Several lights
• TV/computer
• Phone chargers
• Small appliances

A 5,000-watt generator is adequate for emergency essentials but won’t support heating/cooling systems or larger appliances.

Mid-Size Generators (7,000-10,000 watts)

These can handle the basics plus:

• Well pump
• Sump pump
• Microwave
• Toaster oven
• Small window AC unit

Large Portable or Small Standby Generators (10,000-15,000 watts)

These provide enough power for most average homes to maintain comfortable living, including:

• All essentials
• Central air conditioning (smaller units)
• Electric water heater
• Electric range
• Multiple rooms of lighting

Whole-House Standby Generators (15,000-25,000+ watts)

For complete coverage or larger homes:

• 15,000-20,000 watts for an average 2,000-2,500 sq ft home
• 20,000-25,000 watts for larger homes (3,000+ sq ft)
• 25,000+ watts for luxury homes with high-demand appliances

How to Calculate Your Specific Needs

1. List all appliances you want to power during an outage
2. Find running wattage for each appliance
3. Identify starting wattage for motorized appliances (usually 2-3x running wattage)
4. Calculate total wattage needed by adding highest starting wattage to the sum of all other running wattages

Sample Wattage Chart for Common Appliances

ApplianceRunning WattsStarting WattsRefrigerator7002,100Sump Pump8002,400Furnace Fan8002,400Central AC (3 ton)3,50010,500Electric Water Heater4,0004,000Well Pump1,0003,000Lights (per room)60-6000Microwave1,0000Coffee Maker1,0000TV2000

Portable vs. Standby Generators

Portable Generators

• Lower initial cost ($500-$2,500)
• Manually operated
• Requires extension cords or manual transfer switch
• Limited capacity (typically up to 12,000 watts)
• Must be operated outdoors
• Requires fuel storage

Standby Generators

• Higher initial cost ($3,000-$15,000+, plus installation)
• Automatic operation
• Permanently installed with automatic transfer switch
• Higher capacity (7,000-150,000 watts)
• Runs on natural gas or propane (no refueling needed)
• Quieter operation

Common Questions About Home Generators

Will a 22kW generator run my whole house?

For most average homes (2,000-3,000 sq ft), a 22kW generator will power nearly everything, including central air conditioning. However, you may need to manage loads for very large homes or homes with multiple AC units or specialty appliances.

How long can generators run continuously?

• Portable generators: 8-12 hours on a tank of gas
• Standby generators: Indefinitely with natural gas; with propane, depends on tank size

What size generator for 200 amp service?

For a home with 200 amp electrical service, a generator of at least 15-20kW is recommended, though 22-25kW provides more flexibility. Remember that you rarely use your full 200 amp capacity simultaneously.

Do I need to upgrade my electrical panel for a generator?

Not necessarily. Most generators connect through a transfer switch, which can be installed alongside your existing panel. However, older panels may need upgrades to safely accommodate a generator connection.

Installation Considerations

1. Location requirements: Generators need proper clearance from windows, doors, and combustible materials
2. Transfer switch: A licensed electrician should always install your transfer switch as this involves working with your home’s main electrical system and presents significant safety hazards if installed incorrectly
3. Permits: Most localities require permits for permanent generator installations
4. Professional installation: Strongly recommended for standby generators and required for transfer switches

Fuel Considerations

Different generator types use different fuels, each with pros and cons:

• Gasoline: Common for portable generators, but limited shelf life and storage concerns
• Propane: Cleaner burning, indefinite shelf life, but less energy-dense
• Natural gas: Convenient for standby generators, unlimited supply if service remains active
• Diesel: Efficient and durable, but more expensive equipment

The Bottom Line

For a typical home, plan on:

• 5,000-7,500 watts for basic emergency backup
• 10,000-15,000 watts for comfortable living with some limitations
• 15,000-25,000 watts for whole-house coverage

Remember that going slightly larger than your calculated needs provides flexibility and prevents overloading your generator. While the upfront cost is higher, the peace of mind during extended outages is invaluable.

When in doubt, consult with a licensed electrician who can perform a detailed load calculation for your specific home and needs, and always hire a qualified professional to install your transfer switch to ensure safety and code compliance.