Choosing the right generator is not difficult, but you do need to understand your requirements:
Portable or Stationary?
Portable units require you to haul out the unit and plug it in when there is a power outage and require frequent refueling during extended outages
Stationary units can power the entire house or business for extended periods and start automatically when it senses a disruption in power quality
Stationary generators must be installed by licensed professionals, who know the electrical code and local regulations and can perform wiring and plumbing, to ensure that the installation is done correctly
Gas or Diesel?
Gasoline engines are typically found in smaller units and are not intended to be run for long hours or very often
Natural gas generators are a good choice when pipelines are available to deliver gas from a local utility source
Propane-fueled units are an alternative to natural gas, but they will require large propane tanks to be installed to store the fuel
Diesel units are generally more rugged and have longer lives and lower maintenance costs, but require storing large amounts of diesel fuel
Prioritize critical items that you feel must operate during a power outage
Determine which items are inductive loads such as pumps, air conditioners, power tools, garage door openers, dishwashers, and refrigerator/freezers. These loads use electric motors that require two to four times the operating wattage for start-up.
Resistive loads include lights, electric stoves, security systems, radios, televisions, etc. that have the same starting and operating wattages
Using the wattage and nameplate information on motors or appliances, add up the wattage of the devices needed to be covered by the generator.
The total wattage, in 1,000's of watts or kilowatts, plus 15-20% should correspond to the size of the generator in kW.
Engine Type and Features
1,800 RPM water-cooled diesel engines, similar to those found in tractors or trucks, can operate for 20,000 hours or more before major engine maintenance is required and are suitable for commercial or industrial applications.
1,800 RPM water-cooled gas engines are similar to car engines and are typically lighter duty, but will still operate for 6,000 to 12,000 hours with normal maintenance.
3,600 RPM air-cooled gas engines, like those found in most residential generator sets, are similar to lawnmower engines and are the noisiest, can only run for hours rather than days, and have the shortest lives, normally requiring replacement after 500 to 1,500 hours.
Name brand engines allow easy access to parts, service, and support.
Generator sets produce either single or three-phase power. Check your electrical panel or consult an electrician to determine the type of power and voltage required.
Homes and small commercial facilities generally use single phase and 120/240 voltage
Three-phase power is typically found in medium and larger commercial and industrial facilities where power is used for motor starting and running.
The amperage running through the electrical service panels to be covered will also help determine or limit the size of generator and transfer switch that can be used.
Block heaters are required for reliable starting in cold weather
Dead batteries are the most common reason generators do not start. Battery chargers ensure that the units will start when called upon.
Fuel/water separators help protect the engines from water and condensation in the fuel.
Critical-grade mufflers and sound-attenuated enclosures offer quieter operation where noise is a concern.
Load banks are used to test generators to ensure that they will produce their rated capacity when needed.
Remote annunciators and system monitoring and controls allow you to check the status of the generator and transfer switches from inside your office or home.