The short answer is that most homes need somewhere between 7,500 watts for essential circuits and 20,000 watts or more for whole-home backup. The exact number depends on the appliances you want to run, the size of your air conditioning system, and whether you plan to use a portable generator with a manual transfer switch or a permanently installed standby unit. Getting the size right matters. A generator that is too small will overload and shut down when you need it most, and one that is too large wastes money upfront and burns more fuel than necessary.
For homeowners in Lawrenceville, Lilburn, Duluth, Snellville, and the broader Gwinnett County area, this decision carries extra weight. Georgia’s storm season brings severe thunderstorms, tornadoes, and the occasional tropical system, all of which can knock out power for hours or even days. Add in the reality that summer temperatures regularly push past 95 degrees, and losing your air conditioning during an outage becomes more than an inconvenience. Sizing your generator correctly means you can ride out the storm in comfort and safety.
The Difference Between Essential-Circuit and Whole-Home Backup
Before you start adding up wattage numbers, decide what you actually want your generator to power. There are two main approaches, and the one you choose will shape everything else.
Essential-circuit backup means you pick the circuits that matter most and wire only those to the generator through a transfer switch. A typical essentials list includes the refrigerator, a few lighting circuits, the Wi-Fi router, phone chargers, a sump pump if you have one, and maybe a window AC unit or a couple of fans. For most homes, this adds up to roughly 5,000 to 10,000 watts. A quality portable generator or a smaller standby unit in the 7.5 kW to 12 kW range can handle this load.
Whole-home backup means the generator is large enough to power everything in the house, including your central air conditioning, electric range, water heater, and every outlet and light fixture. In a typical Gwinnett County home with a 3-ton or 4-ton central AC system, you may need a standby generator rated at 18 kW to 24 kW or more. Homes with two AC units, an electric water heater, or an EV charger will land at the higher end of that range.
Neither approach is universally “better.” Essential-circuit backup costs less and works well for shorter outages. Whole-home backup costs more but means you never have to think about what you can and cannot turn on. If you have medical equipment that requires continuous power or you work from home, whole-home backup is often worth the investment.
How to Calculate the Wattage Your Home Needs
You do not need to be an electrician to make a reasonable estimate. The process comes down to two numbers for every appliance: running watts and starting watts.
Running watts (sometimes called rated watts) are the continuous power an appliance draws while operating. Starting watts (sometimes called surge watts) are the brief spike of power a motor-driven appliance needs in the first few seconds after it kicks on. A refrigerator, for example, might run at 200 watts but need 1,200 watts to start its compressor. Central air conditioners are the biggest offenders here. A 3-ton central AC unit typically runs at around 3,500 watts but can surge to 5,000 to 7,000 watts on startup.
Here is a practical way to build your estimate. Start by listing the appliances and circuits you want to back up. Look at each one’s nameplate or owner’s manual for wattage information. If the label shows amps instead of watts, multiply amps by 120 (for standard outlets) or 240 (for large appliances like a dryer or AC unit) to get an approximate wattage. Add up all the running watts. Then identify the single largest starting-watt number in your list and add that to the total. The result is a reasonable minimum generator size.
A Quick Sizing Example for a Gwinnett County Home
Say you want essential-circuit backup for a 2,000-square-foot home in Lawrenceville. Your list might look like this: refrigerator (200 running / 1,200 starting), a 5,000 BTU window AC unit (500 running / 1,000 starting), LED lighting on three circuits (300 running), a Wi-Fi router and modem (50 running), garage door opener (550 running / 1,100 starting), phone and laptop chargers (100 running), and a sump pump (800 running / 1,300 starting).
Total running watts: about 2,500. Largest single starting surge: the sump pump at 1,300 watts. Add those together, and you get roughly 3,800 watts as your minimum. A portable generator rated at 5,000 to 7,500 watts would cover this list with comfortable headroom.
Now consider whole-home backup for the same house, but add a 3-ton central AC (3,500 running / 6,500 starting), an electric water heater (4,500 running), and a clothes dryer (5,400 running). Running watts alone jump to about 16,400, and the AC starting surge pushes the peak well above 20,000 watts. A 22 kW standby generator would be a solid fit.
Why Your Electrical Panel Matters for Generator Installation
Your generator does not operate in isolation. It connects to your home’s electrical system through a transfer switch, and the panel itself has to be capable of handling the load. Many older homes in Gwinnett County still have 100-amp electrical panels, which can create limitations when pairing with a larger standby generator.
If your home has a 100-amp panel and you want whole-home backup with a 22 kW generator, your electrician may recommend upgrading your electrical panel as part of the project. This ensures the panel can safely distribute the generator’s output without overloading breakers or wiring. Homes with outdated fuse boxes or panels made by manufacturers with known safety concerns (such as certain Zinsco or Federal Pacific models) will almost certainly need a panel replacement before a generator can be properly connected.
Even if you are not ready for a generator yet, it is worth knowing whether your current electrical service is adequate for your household’s needs. A licensed electrician can evaluate your panel, wiring, and service entrance and tell you exactly where you stand.
Transfer Switches, Permits, and Why Professional Installation Is Required
Every generator that connects to your home’s wiring needs a transfer switch. This device isolates your home from the utility grid when the generator is running. Without it, electricity from your generator can flow backward onto power lines, a phenomenon called backfeeding. Backfeeding is extremely dangerous; it can electrocute utility workers who are trying to restore power and can damage your home’s electrical system. The Electrical Safety Foundation International explains generator backfeeding risks in detail, and the danger is real.
There are two main types of transfer switches. An automatic transfer switch (ATS) detects a power outage and starts the generator on its own, transferring your circuits within seconds. A manual transfer switch or interlock kit requires you to go outside, start the generator, and flip the switch yourself. Standby generators almost always include an ATS, while portable setups typically use a manual switch or interlock.
In Georgia, connecting any generator to your home’s electrical system requires a permit from your local authority, whether that is Gwinnett County, the City of Lawrenceville, or another local building department. The work must be performed by a licensed electrical contractor and will be inspected before it receives final approval. This is not optional. Georgia law requires a licensed electrician for this type of modification, and skipping the permit can create code violations, void your homeowner’s insurance coverage, and leave you with an unsafe installation. You can verify Georgia’s licensing requirements for electrical contractors through the Secretary of State’s office.
Portable vs. Standby: Which Makes Sense for Your Situation
Portable generators cost less upfront and can be a good solution for homeowners who only need to keep a few essentials running during occasional outages. A quality portable unit in the 5,000 to 10,000 watt range typically costs $500 to $2,500 for the generator itself. Having a licensed electrician install an inlet box and manual transfer switch so you can safely connect it to selected circuits usually adds another $1,500 to $4,000, though costs vary based on your home’s specific setup.
Standby generators are permanently installed outside your home, run on natural gas or propane, and start automatically. The total installed cost for a whole-home standby system in metro Atlanta typically ranges from $7,000 to $25,000 or more, depending on the generator’s size, fuel line requirements, and whether your panel needs upgrading. The price is higher, but you get hands-free operation, no refueling during an outage, and the capacity to run your entire home, including central air conditioning.
For homeowners who experience frequent outages or have concerns about extended storm-season disruptions, a standby generator is often the better long-term investment. Our guide on how to prepare for tornado season with a standby generator covers more of the practical benefits.
One important safety note for portable generator owners: carbon monoxide poisoning is the leading cause of generator-related deaths. Never run a portable generator indoors, in a garage, or in any enclosed or partially enclosed space. Place it at least 20 feet from windows, doors, and vents, and make sure your home has working CO detectors with battery backup. The Consumer Product Safety Commission’s generator safety guidance is worth reading before you operate any portable unit.
Getting Your Generator Sized and Installed the Right Way
Sizing a generator is part math and part judgment. The math gets you to a wattage number. The judgment comes from an experienced electrician who can evaluate your panel’s condition, your home’s wiring, your fuel options, and whether load management devices can help you get the performance you need from a smaller, more affordable unit. In older Gwinnett County homes especially, there are often factors that a wattage calculator alone will not catch, like undersized wiring, a panel that needs attention, or a gas meter that may need upsizing to feed a larger generator.
If you are thinking about backup power for your home, the best first step is a professional load calculation. A licensed electrician will walk through your home, identify what you want to keep running, measure the actual demand, and recommend a generator size that fits your needs and your budget.
Kalahari Electrical Services helps homeowners across Lawrenceville, Lilburn, Duluth, Snellville, and greater metro Atlanta with generator sizing, installation, transfer switches, and any panel work the project requires. We hold Georgia electrical contractor license EN213186 and handle the permitting and inspections so you do not have to. Give us a call at 678-665-2309 or reach out through our contact page to set up a consultation.
Frequently Asked Questions
What is the difference between essential-circuit and whole-home generator sizing?
Essential-circuit sizing means you select only the most important circuits, such as the refrigerator, some lights, and a few outlets, and choose a generator large enough to run those. This usually falls in the 5,000 to 10,000 watt range. Whole-home sizing means the generator can power everything in the house simultaneously, including central air conditioning, and typically requires 18 kW to 24 kW or more depending on the home’s total electrical load.
Do I need a transfer switch, and can I install one myself?
Yes, a transfer switch is required by the National Electrical Code any time a generator connects to your home’s wiring. It prevents dangerous backfeeding onto the utility grid. In Georgia, installing a transfer switch is permit-required electrical work that must be performed by a licensed electrician. It is not a legal or safe DIY project.
Will installing a generator require me to upgrade my electrical panel?
It depends on your current panel’s capacity and condition. Many older Gwinnett County homes have 100-amp panels that may not support a large standby generator without an upgrade. Homes with outdated fuse boxes or panels from manufacturers with known reliability issues will almost certainly need a replacement. A licensed electrician can evaluate your panel during the sizing consultation and let you know what is needed.
