Whole-House Backup Generator Sizing Calculator
Calculate whole-house emergency generator wattage sizing, running watts vs starting motor surge LRA, 240V amperage, and transfer switch requirements.
Calculated Results
Frequently Asked Questions
What is the difference between running watts and starting surge watts?
Running (rated) watts is the continuous power needed to operate appliances. Starting (surge) watts is the 2-to-3-second burst of extra electrical power needed to start electric motors and compressors against pressure (Locked Rotor Amps - LRA).
How does an AC soft starter reduce generator sizing?
Central air conditioners pull huge starting surge inrush currents (up to 70–90 Amps). Installing a micro-air soft starter reduces AC compressor startup surge by 65% to 70%, allowing a modest 10kW to 14kW generator to easily start a 4-ton AC.
What size generator is needed to power an entire average home?
Most 2,000–3,000 sq ft homes require a 14kW to 20kW standby generator to run central AC, refrigerator, well pump, lights, and electronics simultaneously. Without central AC, a 7,500W to 9,000W portable generator is sufficient.
Why does propane and natural gas deliver lower kW than gasoline?
Natural gas contains less volumetric energy (BTUs per cubic foot) than gasoline or liquid propane. A generator rated at 22 kW on propane typically outputs 19.5 kW when fueled by utility natural gas.