What Can a 3500 Watt Generator Run?
Check the appliances you want to keep on during an outage and see whether a 3,500 W generator can start them and keep them running together.
What can a 3,500 W generator run
E03Scenario A
On a 3,500 W generator
Over by 300 W at the starting peak. Start the big motors one at a time or drop a load.
- Usable capacity (90%)
- 3,150 W
- Running load selected
- 1,950 W
- Peak when the largest motor starts
- 3,450 W
- Does it fit?
- No: drop loads or take turns
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
Formula
How it works
- Usable capacity = generator watts × 0.9 (we keep 10% in reserve so the generator isn't run at its limit)
- Running load = the sum of the running watts of everything you checked
- Starting peak = running load + the largest extra starting surge among the checked appliances
- It fits when the starting peak is at or below the usable capacity
Only the single largest surge is added, because motors rarely start at the same instant. If two big motors kick on together, the peak is higher than this estimate: start them one at a time.
Sources: running and starting watts from manufacturer sizing tables (Generac) and DOE; motors typically draw 2–3 times their running watts to start. The 90% usable margin is our planning assumption.
Appliance watts (checklist data, from specs/calcs_de.py `APPL`)
| Appliance | Running W | Starting W |
|---|---|---|
| Refrigerator | 700 | 2,200 |
| Chest or upright freezer | 500 | 1,500 |
| Sump pump 1/2 HP | 1,000 | 2,000 |
| Well pump 1 HP | 1,000 | 3,000 |
| Furnace fan | 600 | 1,500 |
| Window AC 10,000 BTU | 1,200 | 3,600 |
| Central AC 3 ton | 3,500 | 7,000 |
| Space heater | 1,500 | 1,500 |
| Microwave | 1,000 | 1,000 |
| Lights (10 LED bulbs) | 100 | 100 |
| TV + router | 150 | 150 |
| Electric water heater | 4,500 | 4,500 |
| Coffee maker | 900 | 900 |
| Phone and laptop chargers | 100 | 100 |
| Washer | 500 | 1,200 |
| Electric dryer | 5,000 | 5,000 |
Worked example
A worked example
A 3,500 W generator has about 3,150 W of usable capacity. A refrigerator, a 10,000 BTU window AC and a microwave run at 2,900 W together, which fits. The problem is the start: when the window AC's compressor kicks on, the peak reaches 5,300 W. Verdict: no, it doesn't fit. Drop the microwave while the AC runs, or step up in size. That same trio fits on a 7,500 W generator.
Questions
FAQ
Can a 3500 watt generator run a refrigerator?
Yes. A refrigerator runs at about 700 W and needs about 2,200 W for a moment to start its compressor. That's well inside the 3,150 W we treat as usable. You can add a furnace fan, 10 LED bulbs and phone chargers and the peak is still 3,000 W.
Can a 3500 watt generator run a window AC?
A 10,000 BTU window unit plus a refrigerator runs at 1,900 W, but the AC's start pushes the peak to 4,300 W, over the 3,150 W usable. Some smaller window units or units with a soft-start may work; check the starting watts on your AC's label and enter them in the appliance calculator.
Running vs starting watts: what's the difference?
Running watts are what an appliance draws once it's going. Starting watts are the brief surge a motor needs to get turning, typically 2–3 times the running figure. A generator must cover the running load plus the biggest surge, even if only for a second or two.
Can I run a well pump on a 3500 watt generator?
Not with the refrigerator also on in our table: a 1 HP well pump plus a fridge peaks at 3,700 W. Alone, the pump's 3,000 W start fits. Run the pump to fill the pressure tank, then switch back to the fridge.
What size generator do I actually need?
Check what you need to keep on and let the portable generator size calculator pick the smallest size that starts it. For many homes, the fridge, a furnace fan, lights and chargers fit on 3,500 W.
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