Looking for Reliable UPS for Whitfield Advantage 3

[Iceshack2]

I'm looking for an Uninterruptible Power Supply for my Advantage 3 pellet stove so that it will continue to operate long enough to shut down during a power outage. Looks like the stove needs minimum of 200 watts to continue to run the exhaust and convection fans. I need enough "on battery run time" to ensure the exhaust fan runs long enough to clear the smoke from the burn pot. Unfortunately The units I've looked at (in the 850AV/500Watt range) have very poor reviews. Any recommendations or experience with keeping smoke out of the house if the power goes out very much appreciated