Best Portable Generators for Home Backup and Outdoor Use

Running Watts vs. Starting Watts: Sizing Inductive Motor Loads

The most common sizing failure occurs when homeowners calculate only 'running watts' and ignore inductive starting surges. Resistive electrical loads (like incandescent light bulbs, toasters, and space heaters) draw the same wattage continuously from startup to shutdown.

Inductive loads containing electric motors or compressors (such as refrigerators, deep well pumps, sump pumps, and furnace blowers) require an initial surge of electricity lasting 2 to 3 seconds to overcome rotational inertia and start the motor. This 'starting surge' is typically 2x to 3x higher than running wattage. A 700-watt refrigerator compressor often requires 2,200 starting watts. If your generator lacks sufficient surge capacity, the breaker trips immediately.

Use our interactive Generator Size Calculator to inventory your household appliances and accurately tally running and starting watts.

Gas, Dual-Fuel, and Propane: Choosing Your Fuel

Gasoline: Gasoline provides the highest energy density (approx. 114,000 BTU per gallon), delivering the highest electrical output per engine size. However, gasoline contains ethanol, which absorbs atmospheric moisture and degrades in as little as 30 to 60 days. Storing gasoline in carburetors causes gum and varnish buildup that prevents emergency starting.

Propane (LPG): Propane contains slightly less energy per gallon (approx. 91,500 BTU), producing ~10% lower peak wattage. However, propane stores indefinitely in standard pressurized cylinders without degrading. It burns significantly cleaner, emits far fewer carbon deposits, and leaves carburetors clean and ready to fire instantly.

Natural Gas (NG): Tri-fuel generators connect directly to household utility natural gas meters. While natural gas yields ~15% to 20% lower peak wattage than gasoline, it eliminates the need to store, transport, or pour fuel in the middle of a blizzard.

Inverter vs. Conventional Generators: Total Harmonic Distortion (THD)

Conventional generators use standard alternators producing raw AC electricity governed mechanically by engine RPM. As heavy loads cycle on and off, engine speed fluctuates, producing Total Harmonic Distortion (THD) of 10% to 25%. This 'dirty power' causes microprocessors in modern variable-speed HVAC blowers, refrigerators, smart TVs, and laptops to overheat or malfunction.

Inverter generators use advanced multiphase alternators that generate high-frequency AC, rectify it to DC power, and then invert it through a microprocessor back into a clean 120V 60Hz pure sine wave with THD under 3%. This matches or exceeds the power quality delivered by commercial electric utilities.

Transfer Switches, Interlock Kits, and Safe Connection

NEVER 'backfeed' a generator by connecting it to a household dryer outlet with a homemade suicide cord. Backfeeding is illegal under the National Electrical Code (NEC) and can energize outdoor utility lines, fatally electrocuting utility linemen working to restore neighborhood power.

Safe and legal connection requires one of two systems installed by a licensed electrician:

1. Manual Transfer Switch: A subpanel containing 6 to 10 dedicated circuit switches (refrigerator, well pump, furnace, lights) that physically isolates those circuits from the utility grid.

2. Generator Interlock Kit: A mechanical metal sliding plate mounted on your main electrical panel that physically prevents the main utility breaker and the generator backfeed breaker from being turned on simultaneously.

Always place your generator outdoors at least 20 feet away from doors, windows, and fresh air vents to prevent deadly carbon monoxide gas from seeping indoors.