Sizing guide · July 2026
What size generator
does your home need?
Most homes need between 10 and 24 kW — but the right number depends on what you want running and how much surge your motors pull at startup. Here's how to think about it, and how we size it for real.
The three tiers
From essentials to whole-home
10–14 kW
Essentials
Refrigerator/freezer, furnace blower, sump or well pump, and a handful of lights and outlets. Keeps the critical stuff on without backing up the whole panel.
Fridge · furnace · sump/well pump · lights
16–22 kW
Whole-home comfort
Everything above plus central air conditioning and most everyday loads — the size most families choose so they never have to think about which circuits are live.
Adds central AC · most appliances · outlets
24 kW+
Large or heavy HVAC
Big square footage, two or more AC units, electric heat, an EV charger, or a well plus other high-draw loads. Sized from a real load calculation.
Multiple AC · electric heat · EV · large homes
The math
How to size it in three steps
- 1
Add up running watts. Total the wattage of everything you want on at once — appliances, HVAC, pumps, lights.
- 2
Add 20–25% for surge. Motors (AC, pumps, compressors) can pull up to 3× their running watts for a moment at startup. That margin keeps the generator from stalling.
- 3
Divide by 1,000. That's your kilowatts. Round up to the nearest standard size — and that's the honest way to size, not a square-footage guess.
What size generator do I need for my house?
Most homes land between 10 kW and 24 kW. A 10–14 kW unit covers essentials — fridge, furnace, sump or well pump, and some lights. A 16–22 kW unit covers whole-home comfort including central air conditioning, which is what most families choose. Larger homes with multiple AC units, electric heat, or an EV charger may need 24 kW or more. The right number comes from a load calculation, not a rule of thumb.
How do I calculate what size I need?
Add up the running watts of everything you want to power at once, then add 20–25% on top to cover the surge when motors start (air conditioners, pumps, and compressors can pull up to three times their running watts for a moment at startup). Divide the total by 1,000 to get kilowatts. That surge margin is why sizing by a simple square-footage rule usually gets it wrong — we do the real calculation for your home.
Do I have to back up the whole house?
No. You can back up just the essential circuits with a smaller unit and a sub-panel, which lowers the cost, or back up the whole home with a larger unit and a 200-amp transfer switch so everything simply stays on. Whole-home is the most popular because there's nothing to think about in an outage, but an essentials setup is a smart, cheaper choice for many homes.
What happens if I get a generator that's too small?
An undersized generator can overload when big loads kick on — most modern units will shed or refuse those loads to protect themselves, so your AC might not start, or the generator could trip. Oversizing wastes money and burns more fuel than needed. The goal is right-sized: enough headroom for startup surges without paying for capacity you'll never use.
Air-cooled or liquid-cooled?
Air-cooled units cover most homes and run up to about 26 kW — they're the standard residential choice and the better value. Liquid-cooled units start around 22–24 kW and go much higher; they're for very large homes or the heaviest loads, and they cost more. For a typical home, an air-cooled unit sized to your loads is the right call.
Sized for your home
Skip the guesswork.
A free assessment includes a real load calculation for your Charlotte home — the right size, then an all-in price. See what it costs →
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