To keep the essentials of an average home running during an outage — refrigerator, a few lights, furnace fan, phone and laptop charging, and the Wi-Fi — you need roughly 3,000 to 5,000 running watts. To run most of a typical house at once, including a well pump or window AC, plan on 7,500 to 10,000+ watts. The catch is that motors draw a big starting (surge) spike for a split second, so the right generator is sized on peak surge, not just the running total. The quickest way to size yours is to pick your appliances in the generator wattage tool — it adds the real surge math for you. Here's the reference data behind it.
Running watts vs. starting watts
Every appliance has two numbers that matter:
- Running (rated) watts — the steady draw once it's on.
- Starting (surge) watts — the brief spike when a motor or compressor kicks on. Anything with a motor (fridge, AC, pump, furnace fan) surges to 2–3× its running watts for a fraction of a second.
A generator has to cover the largest single surge stacked on top of everything already running. That's why two houses with the same running total can need very different generators — the one with a well pump and central AC has far higher peak surge.
Appliance wattage chart
Typical 2026 figures for common household loads:
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator / freezer | 700 | 2,200 |
| Furnace fan (½ HP) | 800 | 2,350 |
| Sump pump (½ HP) | 1,050 | 2,150 |
| Well pump (½ HP) | 1,000 | 2,100 |
| Window AC (10,000 BTU) | 1,200 | 3,600 |
| Central AC (2 ton) | 3,800 | ~11,000 |
| Microwave | 1,000 | 1,000 |
| Coffee maker | 1,000 | 1,000 |
| Toaster | 1,200 | 1,200 |
| Dishwasher | 1,500 | 1,500 |
| Washing machine | 1,200 | 2,300 |
| Electric water heater | 4,000 | 4,000 |
| Space heater | 1,800 | 1,800 |
| Lights (per room) | 60–300 | — |
| TV | 100–300 | — |
| Laptop / phone charging | 50–100 | — |
| Wi-Fi router + modem | 20 | — |
Resistive loads (heaters, toasters, incandescent lights, electric water heaters) have no surge — running and starting watts are the same. Motor-driven and compressor loads are where the surge spikes come from.
Three backup tiers
Tier 1 — Essentials only (3,000–5,000 W). Refrigerator, furnace fan, sump pump, lights, Wi-Fi, and device charging, run one large appliance at a time. A 3,500–5,000 W portable or a small inverter generator covers this. This is what most homeowners actually need to ride out a storm.
Tier 2 — Essentials + comfort (6,000–8,000 W). Adds a window AC or space heater, the microwave, and a well pump without careful load juggling. A 7,000–8,000 W generator is the sweet spot for most single-family homes.
Tier 3 — Whole-home (10,000 W+). Runs central AC, electric water heating, and the kitchen simultaneously — usually a standby generator on a transfer switch, not a portable. Costs and fuel use climb steeply here.
Because the appliance running-cost calculator uses the same wattage figures, you can also see what each of these loads costs to run per hour at your state's electricity rate.
Size it for your house
Don't guess from a total — the surge math is what determines whether the generator stalls when the fridge and well pump kick on together. The generator wattage tool lets you check off exactly the appliances you want to back up and returns the running watts, the real peak surge, and the generator size that covers both. If you're sizing for a specific set, the what-runs-on-X pages show what a given generator size can actually power.
Rule of thumb: most homes are well served by a 7,500-watt generator — enough to run the essentials plus one big load with surge headroom. Only go to a 10,000 W+ standby unit if you need central AC or electric heat during an outage.
Wattages are typical 2026 estimates for planning and vary by model — check your appliance nameplate for exact figures before buying a generator.