What Will a Generator Run?
Short answer: what a generator runs is set by its running watts (the steady load it carries) and its surge watts (the brief startup spike it can absorb). Roughly: a 2,000W inverter runs a fridge plus lights and electronics; a 3,500–4,000W unit adds a furnace blower and a sump pump; a 5,000–6,500W unit adds a well pump and a window AC; a 7,500–9,000W unit starts to handle central AC with care; and a 10,000–22,000W standby runs a whole house. The trick is that only one motor starts at a time, so you size for the running total plus the single largest surge — not the sum of everything.
“What will a 5,000-watt generator run?” is the most-asked generator question, and almost every answer gets it wrong by reading the watts on the box as if they were the whole story. They aren’t. A generator’s real capability is two numbers — the steady running watts it holds, and the brief starting (surge) watts it can deliver for a fraction of a second when a motor kicks on. Below is what each common size actually powers, grounded in real appliance wattages and the same running-plus-largest-surge method our free calculator uses.
First, how to read the chart: two numbers, one rule
Every motor-driven appliance has a running figure (steady draw once it’s going) and a starting figure (the surge a motor demands the instant it switches on, often two to three times higher and gone in a fraction of a second). Resistive loads — lights, a microwave, a space heater, an electric water heater — have no motor, so their starting and running watts are the same. The full explanation is in our running vs starting watts guide.
The one rule that decides what a generator runs: add the running watts of everything on at once, then add only the single largest starting surge on top. Only one motor starts at any given moment, so you never sum every appliance’s surge — that mistake makes people buy far more generator than they need, just as ignoring the surge entirely makes them buy too little.
Appliance wattage chart
Build your own load list from these typical figures. Your generator runs a set of appliances when its rated watts cover their running total and its surge watts cover that total plus the biggest single startup spike.
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator / freezer | 150–800 | ~1,200 |
| Furnace blower (gas, 1/4–1/2 hp) | 600–875 | 1,000–2,350 |
| Sump pump (1/3–1/2 hp) | 800–1,050 | 1,300–2,150 |
| Well pump (1/3–1/2 hp) | 750–1,000 | 1,400–4,000 |
| Window AC (10,000 BTU) | 1,500 | 2,200 |
| Central AC (~3 ton) | 3,500–4,100 | 5,000–6,000 |
| Electric water heater | 4,500 | 4,500 |
| Microwave | 1,000–1,500 | 1,000–1,500 |
| Sump/well pump soft-started | same running | cut by ~half |
| Lights (each) | as marked (e.g. 60W) | same |
| TV / media | 120–300 | 120–300 |
| Internet (modem + router) | 10–30 | same |
Typical ranges, from Honda Power Equipment and DonRowe appliance charts — always confirm your own appliance’s nameplate, since motor sizes vary.
What each generator size will run
These tiers apply the running-plus-largest-surge rule to the chart above. Conventional generators publish a surge rating roughly 20–25% above their running rating; inverter and standby units vary, so always check both numbers on the unit you’re considering.
2,000-watt inverter (~2,000 running / ~2,000–2,200 surge)
Runs: a refrigerator or a furnace blower, plus lights, internet, phone/laptop charging, and a small TV. Won’t run: a well or sump pump, a window or central AC, or a microwave at the same time as the fridge — the stacked surges exceed it. This is the camping/RV and bare-essentials tier: quiet, fuel-efficient, one big appliance at a time.
3,500–4,000-watt portable (~4,000–5,000 surge)
Runs: the real essentials set at once — fridge, gas furnace blower, several lights, TV, internet, and an intermittent microwave — plus a sump pump, because its ~2,000W surge fits under the headroom. This matches Honda’s own worked example, where a fridge, furnace fan, lights, TV, and microwave run on a 3,000-watt unit since the largest single surge is about 1,600 watts. Won’t reliably run: a well pump with a large surge alongside everything else, or any AC.
5,000–6,500-watt portable (~6,000–8,000 surge)
Runs: the essentials plus a well pump (its 1,400–4,000W surge fits the headroom), and a window AC unit run on its own. This is the popular “outage” size for a home with a pump. Won’t run: central air conditioning or an electric water heater — a 3-ton central AC alone needs a ~5,000–6,000W surge, which eats the whole generator.
7,500–9,000-watt portable (~9,000–11,000 surge)
Runs: the essentials, a well pump, and a central air conditioner — especially with a soft starter, which cuts the AC’s startup surge by roughly half. This is the comfortable whole-essentials-plus-comfort tier for most homes that don’t heat with electricity. Won’t cover: simultaneous central AC and electric heat or an electric range pulling at full draw.
10,000–22,000-watt standby
Runs: a whole house. A 10,000–14,000W standby carries the essentials, pumps, central AC, and an electric water heater for a modest home; an 18,000–22,000W standby runs a typical full home including central AC, electric heat, and an electric range without you managing what’s on. Standby units are permanently installed, start automatically, and run on natural gas or propane — whole-house coverage with no load-juggling.
The surge is what trips an “adequate” generator
The number that catches people out is the startup surge. A generator can show plenty of running-watt headroom and still stall the moment a motor kicks on, because that motor briefly demands two to three times its running watts — for some induction motors, three to seven times. A refrigerator running at 200 watts spikes to about 1,200 watts; a 1/2 hp well pump running near 1,000 watts can surge to 2,100–4,000 watts. If that instantaneous spike passes the generator’s surge rating, it trips, no matter how comfortable the steady load looked. A soft starter on the AC or pump ramps the motor up gradually and can cut that surge by half or more, often letting a smaller generator run a load it otherwise couldn’t start.
Frequently asked questions
Will a 2,000 watt generator run a refrigerator?
Yes, on its own — a fridge runs on ~150–800W and surges to ~1,200W, within a 2,000W inverter. But once that surge stacks on lights, a TV, and chargers there’s little headroom left, so you run the fridge plus a few low-draw items, not the fridge plus a microwave or a pump.
Will a 5,000 watt generator run a house?
It runs the essentials plus one large motor — fridge, furnace blower, lights, internet, and a well or sump pump — not a whole house. Central AC or an electric water heater alone can need a ~5,000–6,000W surge. Whole-house needs a 10,000–22,000W standby. See whole-house picks.
What will a 10,000 watt generator run?
The essentials, pumps, and a central AC or electric water heater — close to a modest whole home, as long as the biggest motors don’t start at the same instant. A fully loaded home with central AC, electric heat, and an electric range moves up to a 14,000–22,000W standby. See whole-house picks.
How big a generator do I need to run a well pump?
A 1/2 hp well pump runs ~1,000W but surges to 2,100–4,000W, so you usually need a 5,000–7,500W generator to start it alongside the essentials without stalling — or add a soft starter to cut the surge. See running vs starting watts.
Related: Generator Sizing Calculator · What Size Generator Do I Need? · Running vs Starting Watts · Best for a Power Outage · Best for a Whole House