Sizing guideline — confirm with a transfer switch installer
Generator Size Calculator
Check off the appliances you want to keep running during an outage — this adds up their running watts plus the largest single starting surge, since a generator has to handle both at once.
1. Must-Run Appliances
2. Generator Sizing
Running + largest surgeTOTAL RUNNING WATTS
0 W
PEAK WATTS (WITH STARTING SURGE)
0 W
Suggested generator size: Select your must-run appliances to see a suggestion.
Never plug a generator directly into a wall outlet or your panel. Backfeeding can energize utility lines and injure line workers. A permanent generator setup needs a properly installed and permitted transfer switch.
Why starting surge matters
- Motors (fridges, sump pumps, furnace blowers, well pumps) draw a short burst well above their running wattage when they first start.
- A generator needs enough peak capacity to handle its largest single starting surge on top of everything else already running.
- Running multiple large motors on staggered timers, rather than all starting at once, can let you get by with a smaller generator.
Backup power math
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The Riley Group Electrical provides licensed, insured electrical services across Durham Region and the GTA. For panel upgrades, EV chargers, renovations, or troubleshooting, reach out today.
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Durham Region & the GTA