The Two Ignition Types
A standing pilot burns continuously and generates its own millivolt current through a thermopile. It needs no house power at all, and it will light and run in an outage.
Electronic ignition lights on demand, which saves gas the rest of the year. Most such units carry a battery backup that takes over automatically—but an empty battery compartment is a fireplace that doesn't light.
What the Fan Does
Blowers need house power in nearly every case. Without one, a unit still radiates through the glass—noticeably less heat, spread less far, but real heat all the same.
If outage performance matters, ask how the unit behaves with the fan off. It's a very different number.
Why it Comes up in Utah
Canyon wind events and heavy wet snow take lines down, and the outages that follow land on the coldest nights. In the mountain towns this is a routine planning question rather than a hypothetical.
If a fireplace is meant to be your backup heat, say that on the first visit—it changes the recommendation more than any styling preference.
Two Things Worth Confirming
That the model you're buying has battery backup, and where the compartment is. And whether your thermostat or remote also needs power to call for heat—some do, which can strand an otherwise capable appliance.