HOW TO CHOOSE A GENERATOR.
First let's go over the different types that are out there. Home generators can be portable or stationary (standby). They run on a variety of fuels, such as gasoline, diesel, natural gas (NG), and liquefied petroleum gas (LPG). Each type has its pros and cons. Portable gas models are relatively cheap.
For example, you can buy a 4000W set for $300-$400. However, such devices have short run time: you would need to refill their tank several times a day if you run them continuously at rated load. In addition to this, they are not suitable as a long-term power backup since the pumps may not work during a wide spread blackout. For a long term emergency consider standby sets. They can provide continuous power for the home because they are hooked up to an external fuel source, such as NG line. Some portable devices can also be fueled from an external source and can therefore provide extended run time too. The main differences between them and stationary models are in their connection and activation. A portable device has to be rolled out from the storage, filled with fuel or hooked up to a fuel line, manually started, and connected to your loads. A fixed standby generatorby contrast is already connected to both the house wiring and the fuel source. Therefore it can start immediately either by a push of a button or automatically. Automatic systems have an auto transfer switch. It can sense a power outage, isolate your electrical wiring or designated emergency circuits from the grid, and start the genset. When grid voltage is restored, such a system will connect you back to the utility lines and will turn itself off. You don't even have to be at home to activate it. Note that the typical transfer time of an automatic system is 10-30 seconds. Therefore, if you run important computer applications, you may still need a UPS. It can prevent data loss during the transfer time. Note that even though permanently installed natural gas powered gensets can provide practically unlimited run time, you still need to periodically shut them down to change the motor oil. With some engines you will need to do it as often as every 50-100 hours of operation. This is another reason why a UPS will be useful.
In addition to the convenience of an auto starting option and practically infinite run time, permanently connected standby systems offer power levels higher than portables. Their rating ranges anywhere from 5 kilowatt up into hundreds of kW. Such systems also increase the value of the house. All this makes them the best whole house generators for power outages, especially for the long-lasting ones. Of course, they are more expensive and require professional installation, which are their main disadvantages. If you want something that can be used right away, obviously, a portable device is your only choice.
So, what to look for when you are choosing a generator for the home? Aside from wattage and cost, the main things to consider are the duration of time you may need emergency power, fuel availability, and convenience of use.