Whole-House Generator Sizing Calculator
Calculate continuous running watts and inductive peak starting (surge) watts to size the right standby or portable emergency backup generator.
1. Select Essential Appliances & Loads6 selecionados
Check the appliances you need during grid blackouts to calculate continuous and peak inductive motor surge watts:
2. Central A/C Soft Starter Optimization
Drops locked rotor compressor startup surge by up to 65%, allowing a much smaller and quieter generator to start your central A/C!
Includes a 20% continuous safety buffer per standard electrical engineering codes.
Heavy-Duty Portable Inverter / Tri-Fuel Generator (8,500W – 12,000W)
Cost-effective backup paired with a 50-Amp outdoor inlet box and manual generator interlock kit.
⛽ Estimated 24-Hour Fuel Consumption (50% Load)
Without a soft starter, your central air conditioner requires an additional 4,000+ surge watts, forcing a significantly larger generator!
How it works
1
Select the essential household appliances and circuits you need during power outages.
2
Indicate whether your central air conditioner is equipped with an A/C Soft Starter kit (cutting startup inrush current by up to 65%).
3
Review your minimum recommended generator capacity in kW (factoring in the standard 20% continuous safety buffer).
4
Inspect equipment recommendations (Automatic Standby vs Tri-Fuel Portable) alongside estimated 24-hour fuel consumption.
Frequently asked questions
What is the difference between Running Watts and Starting (Surge) Watts?
Running Watts is the continuous power consumed by an appliance under steady operation. Starting (Surge) Watts is the momentary surge of electrical energy (lasting 2–3 seconds) required to crank inductive motors (A/C compressors, well pumps, refrigerators) from a dead stop.
How does an A/C Soft Starter allow a smaller generator?
Central air conditioners typically produce massive starting surges (often 10,000W to 15,000W LRA). An aftermarket soft starter (e.g. Micro-Air EasyStart) digitally controls the inrush voltage ramp, slashing peak startup current by 60%–70% and allowing a compact portable generator to easily start your central A/C.
Whole-House Standby vs Heavy-Duty Portable: Which is better?
Whole-house standby generators (18kW–26kW) are permanently installed, tap into utility natural gas or large propane tanks, and activate automatically within 10 seconds via an Automatic Transfer Switch (ATS). Portables (8kW–12kW) cost thousands less but require manual rolling, fueling, and cord hookup to a 50A inlet box.
What is a Generator Transfer Switch or Interlock Kit?
A transfer switch or breaker interlock kit is a legally mandated safety mechanism preventing dangerous electrical backfeeding into the utility grid, ensuring lineman safety while safely distributing generator power to your household branch circuits.
Is this tool free?
Yes. The site is supported by ads, so you never pay or need to create an account.
Does it work on mobile?
Yes. The page adapts to your screen and does not require installing any app.