So although they may be clean, and don't emit fumes, the units don't have longevity. They are built similar to the gas units-more parts, more problems. Natural gas may seem to be an easy alternative, because the fuel is unlimited. But the whole idea behind having a generator is to relieve oneself from the shackles of a utility company. Those purchasing a natural gas generator are basically trading in one dependency for another.
Maintenance is also important to maximize the life of any generator.
Similar to a car, there is a certain amount of upkeep needed to prolong the life of each unit. This includes changing spark plugs, oil, air, and fuel filters, and storing fuel properly. The shelf life of gasoline is approximately six months, where diesel can last anywhere from one to three years, by adding quality preservatives. There may also be some problems with storing gasoline, depending on where you live. An accessory that might be a necessity is a transfer switch.