First, you need to decide if you want to power your central air conditioner during a blackout. In the southern states, life can be miserable during a sweltering summer blackout. Northerners might be willing to sacrifice the air conditioner to save some dough.
If you want to run your central air conditioner, you need a strong generator capable of turning over a high-powered motor. If you skimp on strength, don't expect it to start.
To size your central air conditioner, simply take a good look at its metal data plate. It will tell you either its Tons, BTUs or Amps.
If the label is missing, check out your main circuit panel, most air conditioners use either a 30-Amp, 40-Amp or 50-Amp double-pole circuit breaker. The size of the breaker is typically a great indicator to the size of your air conditioner.
For example, if you have a 4-ton (or 48,000 BTU) air conditioner, you'll need at least a 17-kilowatt generator.
You're buying a standby generator to replace the electricity lost from the utility company.
If your electrical panel has a 200-amp main breaker, the maximum amount of electricity your home can consume is 200 amps. If you have 100-amp service, it's 100-amps.
Let's be honest. You're never using the maximum amount of electricity. Your consumption is somewhere between 0 and your maximum.
Do you really need a massive 200-amp generator? In most cases, no. You don't use that much electricity in the first place.