What Size Generator Do I Need to Run a House?
How big a generator does it take to run a house? A guide to essentials-only versus whole-house backup, the watts each appliance draws, and the standby kW class that covers a typical home.
Prices vary by location. Verify with local suppliers.
What size generator do I need to run a house?
There are two answers, depending on your goal. To keep the essentials going in an outage — refrigerator, furnace blower, a well or sump pump, lights and Wi-Fi — most homes need about 5,000–7,500 running watts, which a mid-size portable covers. To run the whole house including central air conditioning, you need a home standby generator of 18–26 kW. Check the appliances you actually want to run in the calculator above and it names the size.
Generator size by home
| What you want to run | Running watts | Generator size |
|---|---|---|
| Essentials (fridge, heat, a pump, lights) | 5,000–7,500 W | 7,500 W portable |
| Essentials + a window AC | 7,500–9,500 W | 9,500 W portable |
| Most of a mid-size home | 10,000–13,000 W | 12,500 W portable / 14 kW standby |
| Whole house, one central AC | 16,000–22,000 W | 20–22 kW standby |
| Large home, multiple AC / electric heat | 22,000–26,000 W+ | 24–26 kW standby |
Why starting watts matter
A generator has to cover both the steady running watts and the brief starting surge when a motor spins up — a well pump, AC compressor or fridge pulls two to three times its running watts for a split second. Because they don’t all start at the same instant, you size to the running total plus the single largest surge, with headroom. That’s exactly what the calculator does.
Once you know the size, compare units on the best whole house generators and best portable generators pages, or see the quick-reference generator size chart.
Planning estimate only. A whole-house standby must be sized with a load calculation and installed by a licensed electrician (NEC). Never run a portable generator indoors or in a garage — the exhaust contains carbon monoxide.
Frequently asked questions
What size generator do I need to run a whole house?
To run a whole house including central air conditioning, most homes need a home standby generator of 18–26 kW, with 22–24 kW the common choice. A 2,000–3,000 sq ft home with one central AC usually lands at 22 kW; larger homes or multiple AC units go to 24–26 kW. Size it to your total running load plus the largest starting surge, then have an electrician confirm with a load calculation. The calculator on this page does the wattage math for you.
Can a portable generator run a whole house?
A portable generator can run a home’s essentials — refrigerator, furnace blower, a well or sump pump, lights and Wi-Fi — through a transfer switch or interlock, but it generally can’t run central air conditioning and the whole house at once. For that you want a home standby generator. A large 9,500–12,500 W portable is the upper end of what a portable practically covers.
What size generator for a 2000 sq ft house?
For a 2,000 sq ft house, essentials backup (fridge, heat, a pump, lights) needs roughly 5,000–7,500 running watts — a mid-size portable. To run the whole house including central AC, plan on a 20–22 kW home standby generator. Square footage is only a rough guide, though; what really sets the size is which appliances you run at once, so use the calculator to add up your actual load.
Will a 12000 watt generator run a house?
A 12,000-watt (12 kW) generator will run most of a house’s essentials and often a central AC unit, but usually not everything at once in a large home. It’s a strong large-portable or small-standby size — good for a house that wants heavy backup without a full whole-house standby. Add up your running watts plus the biggest motor surge to see whether 12 kW clears your peak load.