Determine your peak-wattage needs. Check the owner's manual to determine an appliance's peak wattage. This is how much power it takes to run at its highest level of power consumption, usually when appliances are first starting up. To determine whether your portable generator has the juice it needs to power up your appliances simultaneously, add the peak wattage of all the appliances you want to run. The sum must be less than your portable generator's listed peak output.
Calculate your continuous-wattage requirements. You may not need to start your appliances all at once, but your portable generator will need to provide a steady stream of electricity to keep everything on. You'll need to calculate your continuous wattage. This figure should also be listed in your owner's manual, or you can use an online calculator like the one at ConsumerReports.org.
Will you need to power sensitive electronics? Ordinary generators can create power surges that will fry delicate electronics like computers and flat-screen TVs. For these, it's best to choose an inverter generator; these are usually smaller and more expensive, but they provide smooth, continuous power.
Don't run a generator indoors. Portable generators release potentially harmful carbon monoxide emissions. They should not be operated indoors, in garages, basements, attics, crawl spaces or sheds, according to the U.S. Consumer Product Safety Commission (CPSC).
Keep portable generators high and dry. Like any electrical appliance, portable generators pose a potential electrocution hazard if they're exposed to water. Keep your generator and cords dry and sheltered from the elements, and never handle them with wet hands. The CPSC also recommends protecting your portable generator with "an open, canopy-like structure."
Where will you have your generator serviced? Most generator companies require you to use approved service centers for warranty repairs, and they won't pay for the cost of transporting a generator to and from the service center. In other words, you'll either have to pay the repairman to come to you, or pay for the service company to pick up your generator and then return it. For that reason, the availability of a local servicer can play a key role in your selection of generator brands.