What Size Generator Do I Need for My House?

The Short Answer

For whole-house backup, most homes need a standby generator in the 20 to 26 kilowatt range. If you only want to keep the essentials running — refrigerator, some lights, a few outlets, and your HVAC — a 7 to 10 kilowatt unit usually does the job. The right number for your home depends on its square footage, how many large appliances run at once, and whether you’re powering central air conditioning, which is often the single biggest draw on the system.

Sizing a generator isn’t guesswork, and going too small is a real problem: an undersized unit overloads, trips, and can damage both itself and the equipment plugged into it. Oversizing wastes money and makes the generator run inefficiently. The goal is a unit matched to your actual electrical demand.

How Generator Sizing Actually Works

Generators are rated by their power output in watts or kilowatts (1 kW = 1,000 watts). To size one, you add up the wattage of everything you want to run during an outage, then account for the extra surge of power that motor-driven appliances demand the instant they start.

That startup surge matters more than people expect. An air conditioner or well pump can pull two to three times its running wattage for a split second when the motor kicks on. If your generator can’t supply that surge, it stalls. A proper load calculation looks at both running watts and starting watts.

A Rough Weekend of Wattage

To picture the math, here are typical running figures for common household loads:

• Central air conditioner (3–4 ton): 3,500–5,000 watts, with a much higher startup surge
• Refrigerator: 600–800 watts
• Well or sump pump: 1,000–2,000 watts
• Electric water heater: 3,000–4,500 watts
• Lights and small electronics: 1,000–2,000 watts combined

Add those up, factor in surges, and you can see how a home running AC through an Oklahoma summer climbs toward that 20 kW-plus range quickly.

Whole-House vs. Essentials-Only

There are really two philosophies, and your budget and comfort priorities decide between them.

Essentials-only backup pairs a smaller generator with a transfer switch that feeds a handful of critical circuits. It’s the affordable route and keeps your food cold, a few rooms lit, and key devices charged. The tradeoff is that you’re deciding in advance what stays on.

Whole-house backup uses a larger standby generator wired to your electrical panel through an automatic transfer switch. When the power drops, it starts on its own within seconds and runs everything, including central air. In our climate, that AC coverage is the deciding factor for a lot of families — losing cooling during a July heat wave or a storm-driven outage is more than an inconvenience.

Why Central Oklahoma Homes Lean Larger

Our storm season is exactly why standby generators are popular here. Spring and summer bring the ice, wind, and lightning that knock out power, sometimes for days. And because those outages often coincide with extreme heat or cold, air conditioning and heating aren’t luxuries you can shed to save wattage — which pushes many homeowners toward whole-house sizing.

There’s also fuel to consider, since it shapes both sizing and placement. Most standby units run on natural gas or propane. Natural gas offers an essentially unlimited supply straight from your utility line, which is ideal for extended outages, while propane requires a tank you’ll need to keep filled. Your fuel choice, the gas line’s capacity, and where the generator sits relative to your panel all factor into a proper installation, which is one more reason a professional assessment beats guessing from an online chart.

The most reliable way to land on the right number is a professional load calculation. A licensed electrician measures your home’s real demand, factors in surge loads, and recommends a unit that won’t leave you short or overpay you into a bigger machine than you need. Correct installation and a properly rated transfer switch are just as important as the generator itself.

If you’re weighing backup power for your home, the licensed team at Triple Play Home Services can size and install a generator built around how your household actually uses electricity. Call us at (405) 500-5333 and we’ll help you find the right fit before the next storm rolls through.