Everything on, including central air
Running a whole house means 240 V loads — central AC, well pump, electric water heater — plus everything you’d normally plug in. Central AC alone usually decides the result.
At this size you’re looking at a home standby generator with an automatic transfer switch, installed by an electrician. If that’s more than you need, list only what must run and let heavy items take turns.
Whole house or essential circuits?
A whole-house setup puts the entire electrical panel on the generator through an automatic transfer switch: nothing to plug in, and it starts on its own when the power fails. It is also the biggest generator and the biggest installation.
An essential-circuits setup uses a smaller transfer switch that feeds only the circuits you choose — fridge, furnace, well pump, some lights and outlets. Most homes with a portable generator are wired this way, and it usually needs a much smaller generator.
Many standby systems add load-management modules that hold big loads such as central air or an electric water heater until there is spare capacity, so a smaller standby unit can still cover the whole house.
How the number adds up
| Appliance | Running | Starting | Runs |
|---|---|---|---|
| Refrigerator | 700 W | 2,900 W | together |
| Chest freezer | 500 W | 1,500 W | together |
| Microwave (1,000 W) | 1,000 W | 1,000 W | takes turns |
| Furnace fan (1/2 HP) | 875 W | 3,150 W | together |
| Central AC (3 ton) | 3,500 W | 10,500 W | together |
| Well pump (1/2 HP) | 1,000 W | 2,550 W | together |
| Electric water heater | 3,900 W | 3,900 W | takes turns |
| Washing machine | 1,150 W | 2,800 W | takes turns |
| LED lights (10 bulbs) × 2 | 200 W | 100 W | together |
| TV (LED 55") | 150 W | 150 W | together |
| Wi-Fi router + modem | 20 W | 20 W | together |
| Laptop | 150 W | 150 W | together |
| Phone chargers | 25 W | 25 W | together |
| Running load | 11,020 W | everything together + the biggest “takes turns” item | |
| Worst startup moment | 18,020 W | running load + Central AC (3 ton) starting (+7,000 W) | |
| Minimum generator | 13,775 W | rated watts (running ÷ 0.8) · how we size | |
Questions
How do I size for my house exactly?
Open the calculator with this list and remove or add what your home really has. Every change recalculates instantly.
Do I need everything at once?
Rarely. Letting the water heater, washer and microwave take turns is often the cheapest way to a smaller generator.
What about my EV charger?
Most home Level 2 chargers draw about 7.2 kW for hours[1] — more than most portable generators can supply. Charge before the storm instead.
Natural gas or propane for a standby generator?
Natural gas never needs refilling but usually gives a little less power; propane needs a tank and deliveries. Compare both ratings — every standby model in our database lists its output on each fuel.