The question what size generator do I need for my home is one of the most searched questions in the residential backup power category, and one of the most poorly answered. Most online guides respond with oversimplified square footage charts that have limited relationship to a home’s actual electrical demand during an outage. The truth is that two homes of identical square footage can have peak electrical loads that differ by 10,000 watts or more depending on their fuel source configuration, appliance types, and which loads the owner wants to run simultaneously. This guide gives you a real, technically grounded answer based on connected load, not floor area, from a Master Electrician-founded team that sizes generators for real homes every day across all 48 contiguous US states.

What Size Generator Do I Need: Why Square Footage Is the Wrong Starting Point

Square footage is the most commonly cited sizing metric in consumer-facing generator guides, and it is consistently the least accurate. A 2,500 square foot home in Georgia with an all-electric heat pump, electric water heater, and electric range has a peak simultaneous electrical load that can exceed 22,000 watts when everything runs at once. A 2,500 square foot home in Michigan with a gas furnace, gas water heater, and gas range has a peak electrical load during the same outage that may never exceed 12,000 watts. Both homes are the same size. The generator required to cover them adequately differs by 10kW or more.

The correct starting point for answering what size generator you need for your home is a connected load calculation that adds the running wattage of every appliance and circuit you want operational during an outage, then accounts for the startup surge from the largest motor load in the system. That number, plus a 20 percent operating margin, is your minimum generator output requirement. Everything else follows from that number.

IB Lighting’s Master Electrician-founded team performs this calculation with every generator buyer at no charge before any order is placed. The conversation takes less than fifteen minutes and prevents the most common and most expensive mistake in the generator category: a generator sized by a rule of thumb that turns out to be undersized during the first real outage. Browse the full home standby generator collection at IB Lighting here.

The Appliance Load Reference: What Everything in Your Home Actually Draws

Before calculating your specific load, here is the reference data for every major residential appliance category. Use this table to build your home’s specific load profile by marking which appliances you have and which you want operational during an outage.

What Size Generator Do I Need: Sizing by Home Profile

Once you understand the individual load numbers, the practical next step is mapping your home’s specific appliance configuration against the generator output ranges available in the Generac and Kohler residential lineups. Here is how that maps out across the four most common US residential home profiles.

Profile 1: Gas Appliance Home — Most Common US Configuration

A home with a gas furnace, gas water heater, and gas range has the lowest peak electrical demand of any standard residential configuration during an outage. In this home the electrical load list during an outage typically includes: central AC compressor and air handler, refrigerator and freezer, well pump if applicable, sump pump if applicable, whole-home lighting and outlets, and any specialty loads such as a home office, medical equipment, or entertainment system.

Adding the running loads for that appliance set for a typical 2,000 to 3,000 square foot gas-appliance home produces a combined running load between 8,000 and 13,000 watts. Adding the 4-ton AC startup surge of 12,000 to 16,000 watts as the highest inrush event produces a peak demand that a 14kW to 18kW generator handles with comfortable margin above its rated output ceiling. For a gas-appliance home, a Generac 14kW or 18kW or a Kohler 14kW or 20kW is the appropriate sizing range for whole-home coverage. Browse the full Generac lineup here and Kohler lineup here.

Profile 2: Mixed Fuel Home — Gas Heat with Electric AC and Electric Water Heater

A home with a gas furnace but an electric water heater and central air conditioning represents a very common transitional configuration in US residential stock. The gas furnace blower adds only 500 to 900 watts to the electrical load. However, the electric water heater adds 4,000 to 5,500 watts when it is heating, and the central AC draws 3,500 to 5,000 watts running. If the water heater and AC are running simultaneously, which occurs during morning routines in summer, the combined load can push total demand toward the upper end of what a 14kW generator handles comfortably.

For a mixed fuel home with an electric water heater, the answer to what size generator you need for your home is typically a 16kW to 20kW unit. That output range covers the AC and electric water heater running simultaneously alongside refrigerator, lighting, and outlet loads with adequate margin. If the owner is willing to manage the electric water heater as a non-essential circuit and exclude it from the essential load selection, a 14kW unit may be adequate. IB Lighting’s team works through this specific trade-off in the sizing conversation before any order is placed.

Profile 3: All-Electric Home — Highest Demand Configuration

A fully all-electric home with a heat pump or electric forced air system, electric water heater, and electric range represents the highest peak electrical demand scenario in the residential generator sizing conversation. These homes became increasingly common through the 2010s and 2020s as builders and homeowners moved toward electrification of previously gas-powered functions, and they require the largest generator output levels in the residential air-cooled lineup to achieve whole-home coverage.

Building the load calculation for a typical all-electric home: heat pump running at 4,000 to 5,000 watts, electric water heater at 4,500 watts when heating, electric range at a conservative 4,000 watts for partial burner use, refrigerator at 400 watts, lighting and outlets at 3,000 watts, and sump pump at 1,000 watts produces a combined running load of approximately 17,000 to 18,000 watts before startup surge considerations. Adding the heat pump startup surge of 11,000 to 15,000 watts places the peak demand at 28,000 watts or more, which is above what any residential air-cooled standby generator can sustain as continuous rated output.

The practical resolution is that not every all-electric appliance runs at maximum draw simultaneously in real outage conditions. The electric range runs at partial load most of the time. The water heater cycles on and off rather than drawing continuously. The heat pump reaches steady-state running watts quickly after the startup surge passes. A Generac 22kW or 24kW unit paired with Generac’s smart load management module that temporarily sheds the electric water heater and range circuits when total demand approaches the generator’s rated output ceiling is the appropriate whole-home solution for most all-electric homes. IB Lighting sizes this configuration specifically for all-electric homes before recommending it.

Profile 4: Large Home with High-Draw Specialty Loads

Homes above 3,500 square feet with dual HVAC zones, workshops with compressors and high-draw power tools, EV chargers, or pool pumps represent the most demanding sizing scenarios in the residential generator category. The dual HVAC zone scenario is particularly significant because two 3-ton compressors starting in close succession during a hot summer outage can produce back-to-back startup surges that push the combined peak demand above what a 22kW generator handles without a load management module.

For large homes with multiple high-draw loads, the answer to what size generator you need for your home is a Generac 24kW unit, which is the highest-output residential air-cooled standby generator in Generac’s lineup, potentially paired with a load management or smart management module to intelligently shed lower-priority loads during simultaneous peak demand events. Kohler’s 20kW unit with PowerBoost is an alternative configuration that handles large motor starting loads particularly well through Kohler’s above-rated-output startup technology.

Quick Reference: What Size Generator Do I Need by Home Type

The Motor Starting Surge Variable: Why Running Watts Are Not Enough

One of the most important technical variables in answering what size generator you need for your home is motor starting inrush current, and it is the variable that most non-technical sizing guides omit entirely. Every motor-driven appliance in your home draws significantly more current for the fraction of a second it takes the motor to accelerate from zero to operating speed than it draws while running at steady state. This startup surge is what causes lights to dim momentarily when an AC compressor starts. In a generator context, the startup surge from a large AC compressor is the single highest instantaneous electrical demand your generator must handle.

How to Account for Startup Surge in Your Generator Size Calculation

The practical method for accounting for startup surge without overcomplicating the calculation is to identify the single largest motor-driven load in your home, find its startup surge wattage from the reference table above, and add that surge figure to your total running load sum to produce your peak instantaneous demand. That peak instantaneous figure must fall below your generator’s rated output capacity for the generator to handle the startup event without stalling.

For a home whose running load sums to 11,000 watts and whose 4-ton AC has a startup surge of 14,000 watts, the peak instantaneous demand at the moment the AC compressor starts while everything else is also running is 11,000 plus 14,000 equals 25,000 watts. A 14kW generator rated at 14,000 continuous watts cannot handle that instantaneous peak and will stall. A 22kW generator or a Kohler 20kW unit with PowerBoost handles it because their output ceiling or above-rated startup capability exceeds the peak demand event. This is the calculation that determines whether a generator works under real outage conditions, and it is the calculation IB Lighting performs for every generator buyer before recommending a specific model.

The National Electrical Code NEC Article 220 governs branch circuit and feeder load calculations, which forms the technical foundation for the sizing methodology that licensed electricians use in professional generator specification work.

What Size Generator Do I Need: By Coverage Priority

A separate dimension of the generator sizing question is not just what your home can draw but what you actually need to operate during an outage and how that priority list affects the size decision.

Does Home Size Matter at All for Generator Sizing?

Home size is not irrelevant to the what size generator do I need question. It is simply not the primary variable that most guides treat it as. Here is the accurate relationship between home size and generator sizing requirements.

Larger homes tend to have larger HVAC systems. A 4,500 square foot home is more likely to have a 5-ton central AC system or dual 3-ton zones than a 1,500 square foot home. The HVAC system size is a generator sizing variable. Home size correlates with HVAC size, which correlates with generator size, but the connection is through HVAC load, not through square footage directly.

Larger homes also tend to have more circuits and more outlets, which contributes to a higher background lighting and outlet load. But the difference between a 1,500 square foot home and a 4,000 square foot home in this category is typically 1,000 to 2,000 watts of running load, which is much less significant to the sizing decision than the presence or absence of electric versus gas appliances for the major high-draw functions.

The most reliable use of square footage in generator sizing is as a rough screening tool to identify candidate output levels before refining with an actual load calculation. Use the quick reference table above as your starting point, then verify with an actual appliance-by-appliance calculation or with IB Lighting’s team before placing an order.

Portable Generator Sizing vs Standby Generator Sizing

The sizing approach for portable generators differs from standby generator sizing in one important practical way. A portable generator is manually managed during an outage, which means you can shed loads that would overload the unit by simply unplugging or switching off non-essential appliances. A standby generator with a whole-home automatic transfer switch transfers every connected circuit simultaneously, so the generator must be sized to handle the simultaneous load of everything it is connected to, not the carefully managed load of a selective manual connection process.

If you are evaluating a portable generator as a lower-cost alternative to a standby system, the sizing approach involves identifying the essential circuits you plan to connect and their combined running load, then finding a portable generator rated above that combined load with startup surge capacity for the largest motor on the list. IB Lighting carries portable and inverter generators sized for essential circuit coverage. Browse the portable inverter generator range here.

Frequently Asked Questions: What Size Generator Do I Need for My Home

What Size Generator Do I Need for My Home: The Answer in One Sentence

The generator size you need for your home is the output level that covers your home’s peak simultaneous electrical load including the largest motor starting surge, plus a 20 percent operating margin, sourced from a legitimate warranted unit installed by a licensed electrician on a matched automatic transfer switch sized to your main panel amperage.

Everything in this guide builds toward that sentence. The load calculation quantifies the peak demand. The fuel source determines which appliances contribute to that demand. The home profile tables give you a starting range. The motor starting surge variable tells you why running watts alone are insufficient. The coverage priority framework tells you which loads define your minimum functional requirement. And the quick reference table maps all of it to specific generator output levels available from Generac and Kohler through IB Lighting.

Browse the full home standby generator collection here, explore Generac here and Kohler here, or call IB Lighting’s team at (800) 674-9019 to confirm the right size for your specific home before you commit to any order. Transfer switch kits matched to your generator and panel amperage are available at iblighting.com/product-category/generator-transfer-switch-kits.