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Ubify Financial Advisory Board
FINANCIAL ANALYSTS & CPA REVIEWERS
About This Tool
Selecting the right size portable or standby generator for emergency home backup power requires accounting for both continuous running wattage and the momentary startup surge demands of inductive motor loads (such as refrigerator compressors, sump pumps, and furnace blowers).
This sizing tool tallies continuous running wattage across your selected household essentials and adds the single largest motor startup surge differential, ensuring the generator can start heavy inductive equipment without stalling or tripping internal circuit breakers.
For example, powering one standard refrigerator/freezer (700W run / 2200W surge), one submersible sump pump (1000W run / 2100W surge), one forced-air furnace blower fan (800W run / 2000W surge), and 600W of general lighting and electronics requires 3,100 continuous running watts. Factoring in the 1,500W surge differential of the refrigerator compressor yields a peak starting demand of 4,600 surge watts, indicating that a generator rated for at least 5,000 surge watts is required.
All electrical sizing calculations run locally in your web browser. No home equipment lists or appliance details are sent across the network.
How to Use
- 1
Enter the count of refrigerators and freezers you need to power (each rated at 700W running and 2200W starting surge).
- 2
Set whether your home requires emergency sump pump power (1 for Yes, 0 for No).
- 3
Set whether your home requires forced-air furnace blower power (1 for Yes, 0 for No).
- 4
Enter your estimated lighting, Wi-Fi router, TV, and mobile device wattage in watts.
- 5
Read the total continuous running watts, peak starting surge wattage, and recommended generator capacity rounded to the next 500W tier.
Frequently Asked Questions
Why is generator surge capacity calculated using only the single largest motor?
In typical household operation, multiple motor loads do not start at the exact same millisecond. Sizing for the largest single startup surge on top of continuous running loads provides reliable starting capacity without unnecessary generator oversizing.
How much safety headroom should I allow when buying a generator?
It is generally recommended to maintain at least 15% to 20% continuous load headroom above your running watts so the generator does not operate at maximum output continuously.
Are my appliance selections transmitted to a remote server?
No. All wattage formulas execute locally in your web browser with client-side JavaScript.