Running Watts vs Starting Watts for Generator Planning
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Running watts are continuous draw. Additional starting watts are the extra surge above running watts while a motor starts; total starting watts = running + additional. Plan with: sum of running watts + the single largest additional starting watts, assuming one motor starts at a time.
Generator worksheets list two numbers per appliance, and the labels are easy to misread. Getting the arithmetic right avoids buying a generator that stalls when a compressor kicks on — or one far bigger than needed.
Run the numbers with the Generator Wattage Planner.
The three numbers
Example figures — use your nameplate or manual
| Appliance | Running W | Additional start W | Total start W |
|---|---|---|---|
| Refrigerator (example) | 700 | 1,500 | 2,200 |
| Sump pump (example) | 800 | 1,300 | 2,100 |
| LED lights ×6 (example) | 60 | 0 | 60 |
Worked example
Running load = 700 + 800 + 60 = 1,560 W. Largest additional start = 1,500 W, so the one-start peak = 3,060 W. If both motors started at the same instant: 1,560 + 1,500 + 1,300 = 4,360 W. Adding total starting watts for everything (2,200 + 2,100 + 60 = 4,360) happens to match here only because the lights add nothing — with more resistive loads that shortcut double-counts.
Safety essentials
- Run portable generators outdoors only, at least 20 ft from doors, windows and vents, and never in an attached garage (NFPA).
- Install battery or battery-backup CO alarms (CPSC, USFA).
- Do not backfeed through an outlet; connecting to house wiring requires a properly rated transfer switch installed by a qualified electrician (NFPA).
- Let the engine cool before refuelling.
Common mistakes
- Treating additional starting watts as total starting watts
- Ignoring that output can differ by fuel type
- Assuming a worksheet total is an installation size
Assumptions and limitations
Motor inrush varies with the motor and conditions, soft starters reduce it, and 240 V generators split loads across two 120 V legs. Standby installations must be sized and installed by a licensed electrician.