I have to agree with Ginski and Kirk on this one, Harman's reccomendation is a unit from a company called Surefire, they make a unit called the stove sentry which provides an automatic switchover from utility to battery power and back again just as any office type UPS would do. The difference is that they use an external 12V battery such as a deep cycle or gel cell. There are other manufacturers of this type of unit also, Tripp Lite, Xantrex (Heart Interface) come to mind. They are common in the RV industry with people who want AC power while on the road, but don't want to run a generator. Prices on the smaller Tripp Lite unts are in the $300 range new, but can be had on Ebay for less.
To me a generator is only viable if it is fully automatic and will startup and transfer power automatically. These whole house generators can add up to a sizable investment especially if you have to pay someone for installation.
I use a unit from Tripp Lite, an older model called the APS512. I have it attached to a size 29 deep cycle marine battery. It is rated for 500VA continuous and 1000VA surge so it has no problem running my system. I have measured my running current and calculated an 8 to 12 hour run time on battery power. It has an internal charger that adjusts charging current in proportion to battery voltage and wil maintain a float charge when the battery is fully charged. The switchover to battery power is almost instantaneous, and it will swith back to utility power a few seconds after power is restored. It also provides a good degree of surge protection to all the electrical devices that are attached.
My goal with this system was to maintain power to the boiler to keep it lit if the power were to fail. Our power doesn't go out all that often and when it does, its usually for just a few minutes or maybe an hour or two at the most.