Whole house generators basically come in 4 sizes, ranging from 22-48 kilowatts.
You determine your size based on the amount of electricity your home consumes.
The majority of newer homes in the United States are built with 200-amp electrical service.
In other words, the MAXIMUM amount of electricity your home can consume is 200-amps.
In reality, it never really uses every amp of electricity. On hot summer days, the central air conditioner consumes a ton. At night, most homes barely use any.
If you absolutely, positively want to replace every, single amp, you’ll need a 48-kilowatt whole house system, which generates all 200-amps of electricity.
In most cases, however, you can save significant dollars by choosing a smaller model, which could still power the whole house anyway.
Most customers choose one of the four sizes below based on their pocketbook instead of online calculators.
Select a Series
Generac, the leading manufacturer of whole house generators, makes three grades of liquid-cooled generators.
You simply need to select which “series” of generators works best for your home and budget.
Generac Commercial Series
If you find yourself shopping for a
Generac Commercial Series standby generator, you’re in the wrong place.
The vast majority of homes use 120/240-volt, single-phase electricity. Three-phase electricity is designed for commercial applications, such as restaurants and banks.
Don’t even consider a Generac Commercial generator for a whole house application.
Generac QuietSource Series 
The
Generac QuietSource Series includes a few three-phase generators too. Ignore them. Instead, focus your attention on the four 120/240-volt, single phase models.
These premium grade generators include two unique features, definitely worth the extra money.
1. 1800 vs. 3600 RPMs
Huh? Basically, the Generac engines on a QuietSource generator run at half the speed of other whole house generators. The reduced speed consumes less fuel, makes less noise and wears less, resulting in less maintenance and increased life span.
2. Aluminum Enclosure
Just like air conditioners, natural gas or propane powered generators are fully enclosed to protect the generator from the weather, rodents and stray baseballs.
Aluminum enclosures cost a little more, but they also outlast their steel counterparts. If you live near the coast – where salty air is notorious for corroding metal – get an aluminum enclosure.
Generac Guardian Series 
If you want a no-frills whole house generator, consider the
Generac Guardian Series.
These steel enclosed generators are little louder, but they also cost less. They’re designed to accomplish the mission without breaking the bank.
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