How to Size a Standby Generator for Your Home

Start with what you actually need to keep running

Standby generators are sized in kilowatts (kW). The wrong size is the most expensive mistake homeowners make — too small and your generator trips offline during a heat wave, too large and you pay 30–60% more upfront for capacity you never use.

Begin by writing down what you genuinely need during an outage: refrigerator, well pump, HVAC, sump pump, a few lights, internet, garage door. Skip the dryer, electric oven, and EV charger unless you've already decided to back them up.

The 50% rule for whole-house coverage

For a typical 2,000–3,000 sq ft home with central A/C, a 22 kW air-cooled unit covers nearly every essential load with margin. Anything smaller usually requires load shedding (Generac Smart Switches, Briggs Symphony, Kohler Power Boost).

If your central A/C is 3 tons or smaller and you don't have an electric water heater or electric range, you can often get away with 14–18 kW plus a load management switch.

When to step up to liquid-cooled

Homes over 5,000 sq ft, multiple A/C compressors, or any commercial use point you toward liquid-cooled units (typically 25 kW and up). These run cooler under sustained load and last 2–3x longer between major service intervals — but installation runs significantly higher.

Get a real load calculation

An online sizing calculator gets you in the ballpark. A qualified dealer running a proper load calculation against your panel will save you from buying the wrong unit. Most reputable dealers offer this free as part of a site visit.