What size generator to run a house?
For the essentials — fridge, freezer, furnace fan, sump pump, ten LED bulbs, a TV, the router and a microwave — the running total is about 3,640 W. With 25% headroom, plan on 4,550 W running and 4,740 W starting watts.
How to work it out
- Running total 3,640 W × (1 + 25% headroom) = 4,550 W running
- Running total 3,640 W + biggest start-up extra 1,100 W = 4,740 W → 4,740 W starting
“The house” usually means the things you can’t do without in an outage, not every circuit. This list uses the top of Champion’s ranges for each item. Central air, an electric water heater, an electric range or a dryer each add thousands of watts — usually a standby generator’s job.
Adjust for your project
More options: Headroom
- Running watts
- 4,550 W
- Starting (peak) watts
- 4,740 W
- Running watts, all together
- 3,640 W
- Biggest single starting surge (extra)
- 1,100 W
- Running current at 120 V
- 30.3 A
- Over about 3,600 W, a single 120 V 30 A outlet can’t carry it all — you need a generator with 120/240 V output and a connection through a transfer switch, or loads split across several outlets and cords.
- Start the biggest motor first, then add the other loads one at a time — the generator only has to cover one start at once.
Generator size with other headroom
| Headroom on running watts | Running watts | Starting (peak) watts |
|---|---|---|
| 0% | 3,640 W | 4,740 W |
| 10% | 4,004 W | 4,740 W |
| 25% | 4,550 W | 4,740 W |
| 50% | 5,460 W | 5,460 W |
What to know about powering a house in an outage
- Essentials fit a 5,000–6,500 W portable. Champion’s 6500 W dual-fuel model, for example, is rated 6,500 running and 8,125 starting watts on gasoline.
- Central air changes the class. A 3-ton central AC is 3,000–3,500 running and 5,000–6,000 starting watts on Champion’s chart — on top of everything else.
- Connect it properly. Over about 3,600 W you can’t use a single 120 V outlet, and feeding the house panel needs a transfer switch installed by a licensed electrician. Never backfeed through a wall outlet.
- Fuel adds up. Champion rates its 6500 W model at 11 hours at half load on a 7.7-gallon tank — about 17 gallons a day if it runs around the clock. See how long a generator runs on 5 gallons of gas.
Prefer batteries for a quiet outage? How many kWh to power a house for a day sizes a home battery. For just the fridge, see what size generator to run a refrigerator; for the well, what size generator to run a well pump.
Different size? Use the full Generator Size Calculator.
What you’ll need
- Dual-fuel portable generatorPremium price
Runs on gasoline or propane. Propane stores for years without going stale; expect somewhat fewer watts on propane.
See options on Amazon (opens in a new tab) - Battery-operated carbon monoxide alarmBudget price
CPSC advises battery or battery-backup CO alarms whenever a generator is in use. Look for UL 2034 certification and test monthly.
See options on Amazon (opens in a new tab) - Outdoor generator extension cordMid-range price
Lets the generator sit well away from the house. CPSC says to use outdoor-rated cords whose rating exceeds the total load, with all three prongs.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
What size generator to run a house with central air?
About 8,925 W running and 9,640 W starting watts with a 3-ton central AC added — standby-generator territory.
What size generator for just the fridge, furnace fan and lights?
About 1,375 W running and 2,100 W starting watts.
Other common sizes
- What size generator to run a refrigerator — 1,200 W starting — a 2,000 W-class generator
- What size generator to run a well pump — 2,500 W running / 4,000 W starting
Sources
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).
- Virginia Cooperative Extension, BSE-301: Estimating Appliance and Home Electronic Energy Use (2020) (opens in a new tab) — Wattage × hours ÷ 1,000 = kWh per day; watts = amps × volts when only amps are listed; a refrigerator runs at full wattage about a third of the time; typical nameplate wattages.
- ENERGY STAR — Certified Televisions data set (on-mode power) (opens in a new tab) — Certified models, on-mode watts, retrieved October 2026: 32 in about 27–36 W; 43 in about 45–78 W; 50 in about 61–90 W; 55 in about 64–114 W; 65 in about 85–135 W; 75 in about 120–176 W.
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.
- U.S. Consumer Product Safety Commission — CPSC Warns Consumers in Path of Storms to Take Precautions When Using Portable Generators (July 24, 2020) (opens in a new tab) — “Use your generator OUTSIDE your house ONLY, at least 20 feet from your home”; make sure you have working CO alarms.
- OSHA Fact Sheet — Using Portable Generators Safely (opens in a new tab) — Never attach a generator to a building’s wiring unless a qualified electrician has installed a transfer switch; 3–4 ft of clear space around the unit.
- Champion Power Equipment — 3500-Watt Dual Fuel Generator (model 201213) specifications (opens in a new tab) — 3,500 running / 4,000 starting watts on gasoline; 14 h at 50% load on 4.7 gal; 10.5 h at 50% load on a 20 lb propane tank; 120 V 30 A TT-30R RV outlet.
- Champion Power Equipment — 6500-Watt Dual Fuel Generator (model 201077) specifications (opens in a new tab) — 6,500 running / 8,125 starting watts on gasoline (5,850 / 7,325 on propane); 11 h at 50% load on 7.7 gal; 6.5 h at 50% load on a 20 lb propane tank.
- Champion Power Equipment — 2000-Watt Dual Fuel Inverter (model 201230) specifications (opens in a new tab) — 1,700 running / 2,000 starting watts on gasoline (1,530 / 2,000 on propane); 11.5 h at 25% load on 1.05 gal; 34 h at 25% load on a 20 lb propane tank.