There are two types of generators that can be used to power a house: portable generators are mobile, gas-powered, and must be manually started. Standby generators are usually stationary, gas or propane powered, and automatically start during power failures.
There are pros and cons to each type of generator. Portable generators are the least expensive, generally costing between $500 to $1,500, as of 2015. However, they can be inconvenient, as someone must be present at all times to monitor and fill them with gas. Portable generators are also less powerful than their counterpart, only being able to power a few appliances.
Automatic standby generators are more expensive, with prices starting at around $5,000, but are also less of a hassle to use. They can run on natural gas or a propane tank and do not require someone to monitor them at all times. Standby generators are also powerful enough to keep most household appliances running.