How to read this chart
Two columns, and they do different jobs.
Running watts is what the appliance draws once it is going. Add these up for everything that runs at the same time — this decides whether the machine can carry your house continuously.
Starting watts is the surge a motor demands for a fraction of a second at startup, typically two to three times its running draw. You do not add these up. Motors almost never start at the same instant, so take only the single largest starting figure on your list.
The formula: total running watts, minus the running watts of the item with the biggest surge, plus that item's starting watts. That is your peak requirement.
The chart
Refrigeration and food
| Appliance | Running watts | Starting watts |
|---|
| Refrigerator | 150–400 | 800–1,200 |
|---|
| Freezer | 100–500 | 500–1,000 |
|---|
| Microwave | 600–1,200 | — |
|---|
Heating and cooling
| Appliance | Running watts | Starting watts |
|---|
| Furnace fan (½ HP) | 300–800 | 800–1,600 |
|---|
| Furnace fan (⅛ HP) | 300 | 500 |
|---|
| Furnace fan (⅙ HP) | 500 | 750 |
|---|
| Furnace fan (¼ HP) | 600 | 1,000 |
|---|
| Furnace fan (⅓ HP) | 700 | 1,400 |
|---|
| Window AC (5,000 BTU) | 450–600 | 900–1,200 |
|---|
| Window AC (10,000 BTU) | 900–1,200 | 1,800–2,400 |
|---|
| Central AC (2 ton) | 2,000–2,500 | 3,500–4,500 |
|---|
| Central AC (3 ton) | 3,000–3,500 | 5,000–6,000 |
|---|
| Central AC (4 ton) | 4,000–5,000 | 6,500–8,000 |
|---|
| Space heater | 750–1,500 | — |
|---|
| Electric water heater | 3,000–4,500 | — |
|---|
Pumps
| Appliance | Running watts | Starting watts |
|---|
| Sump pump (⅓ HP) | 500–800 | 1,000–1,600 |
|---|
| Sump pump (½ HP) | 800–1,050 | 1,300–2,150 |
|---|
| Well pump (½ HP) | 750–1,000 | 1,500–2,000 |
|---|
| Well pump (1 HP) | 1,000–2,000 | 2,000–4,000 |
|---|
Electronics, lighting and medical
| Appliance | Running watts | Starting watts |
|---|
| LED bulb | 8–15 | — |
|---|
| TV (32–55 in) | 80–400 | — |
|---|
| CPAP (no humidifier) | 30–60 | — |
|---|
| CPAP (heated humidifier) | 60–120 | — |
|---|
Sources. All figures except the furnace-fan-by-horsepower rows are from Champion Power Equipment's published generator wattage chart. The furnace-fan-by-horsepower breakdown comes from Honda Power Equipment's wattage estimation guide. Ranges are the manufacturers' own. We have not measured any appliance ourselves, and where a manufacturer publishes no figure the cell is left blank rather than filled with an estimate. Router and modem draw is not published in either reference; the roughly 20W figure used elsewhere on this site is taken from equipment power-supply ratings and is flagged as such wherever it appears.
Two worked examples
A house with a basement
- Refrigerator — 400W running, 1,200W starting
- Furnace fan, ½ HP — 800W running, 1,600W starting
- Sump pump, ⅓ HP — 800W running, 1,600W starting
- Six LED bulbs — 90W running
- Router and modem — about 20W
Running total: 2,110W. Largest starting surge: the furnace fan or the sump pump at 1,600W. Peak: 2,110 − 800 + 1,600 = 2,910W.
So a 3,500W generator covers it, and a 3,000W battery inverter is marginal. Note that using the top of every published range is deliberately conservative — with mid-range appliances the same house lands nearer 1,500W running.
A house on a well, in summer
- Refrigerator — 400W running, 1,200W starting
- Well pump, 1 HP — 2,000W running, 4,000W starting
- Window AC, 10,000 BTU — 1,200W running, 2,400W starting
- Six LED bulbs — 90W running
Running total: 3,690W. Largest surge: the well pump at 4,000W. Peak: 3,690 − 2,000 + 4,000 = 5,690W.
That eliminates every battery on this site and points at a 7,500W generator or larger. The well pump alone is the reason.
Load shedding is free capacity
Both examples assume everything runs together. In an actual outage that is not how it works — you run the fridge and the sump pump, and you run the microwave for four minutes with the furnace off.
Deciding in advance which two things share the machine routinely halves the generator you need and halves what it costs to fuel. It is the cheapest capacity available and it costs nothing but a plan.
Where these numbers come from, and their limits
These are manufacturer reference figures, published for exactly this purpose. They are ranges because appliances vary enormously — a 2003 side-by-side refrigerator and a 2024 Energy Star model differ by a factor of two or more.
Your own appliance publishes its real number. Look for the nameplate — usually a sticker inside the door, on the back, or on the motor — which gives volts and amps. Watts = volts × amps. A fridge labeled 115V and 6A draws 690W at full compressor draw, though its average over a duty cycle is far lower. That nameplate figure beats any chart, including this one.
Once you have your peak number, the sizing page turns it into a machine, and the duration page decides whether that machine should be a battery or a generator.
