Start with an honest load list
Separate must-run equipment from conveniences. Record each item’s published running watts and starting watts from its nameplate or manual. If only volts and amps are listed, multiplying them gives an approximate volt-amp load, but manufacturer wattage is preferable because motors and electronic loads are not always simple resistive loads.
Running and starting watts
Running watts are continuous demand; starting watts cover the short surge from compressors, pumps and motors. Add the running loads that will operate together, then allow for the largest likely additional starting surge. Do not simply shop by the biggest headline number on the box, which is often a temporary peak rather than sustainable output.
Voltage and load management
A 240-volt well pump or home inlet requires the correct 120/240-volt generator and connector. Adequate total wattage does not prevent one 120-volt leg from being overloaded. Scheduling a microwave, water heater, pump or air conditioner at different times can reduce the generator size you need.
Leave usable margin
Reasonable headroom prevents continuous operation at the limit and allows for small unlisted loads. Compare runtime claims at equivalent load percentages, and confirm fuel-specific ratings because dual- and tri-fuel machines commonly produce different output on gasoline, propane and natural gas. Before feeding household wiring, have a qualified electrician confirm the generator, inlet and transfer equipment.
Sources and further reading
- U.S. CPSC portable-generator guidance
- Honda generator selection guide
- Briggs & Stratton wattage guidance
Confirm current specifications and all operating instructions in the manufacturer manual. Electrical work should follow local code and be completed by a qualified professional.